Muscarinic receptor agonist in combination with a vesicular monoamine transporter 2 inhibitor, for use in the treatment of a neurological or psychiatric disorder

Abstract

Provided are methods of treating a neurological or psychiatric disease or disorder, methods of treating behavioral problems associated with a neurological or psychiatric disease or disorder, and methods of improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder in a subject in need thereof.

Description

[0001] MUSCARINIC RECEPTOR AGONIST IN COMBINATION WITH A VESICULAR MONOAMINE TRANSPORTER 2 INHIBITOR, FOR USE IN THE TREATMENT OF A NEUROLOGICAL OR PSYCHIATRIC DISORDER

[0002] FIELD

[0003] This disclosure provides pharmaceutical combinations of a muscarinic acetylcholine M4 receptor agonist and a vesicular monoamine transporter 2 (VMAT2) inhibitor, pharmaceutical compositions comprising such combinations, and methods of using such combinations for the treatment of neurological and psychiatric diseases and disorders and other related diseases or conditions described herein.

[0004] BACKGROUND

[0005] Muscarinic acetylcholine receptors are G-protein coupled receptors (GPCRs) widely expressed both in the central nervous system (CNS) and the periphery. Depending on the muscarinic receptor subtype (M1-M5) and location, they mediate a variety of physiological functions. Individual subtypes differ in signaling profiles. Subtypes Ml, M3, and M5 preferentially activate the Gq / 11 class of G-proteins, while M2 and M4 preferentially activate inhibitory Gi / o G-proteins. The flexible G-protein interface of muscarinic receptors allows them to interact with several types of G-proteins with varying efficacy, potency, and kinetics. Moreover, muscarinic receptors can also couple to G-proteins from other classes.

[0006] Disruption of muscarinic signaling often contributes to pathologies in the CNS and periphery making muscarinic agonists potential tools for the treatment of a variety of pathologies. Importantly, selective modulation of individual subtypes of muscarinic receptors is necessary to avoid undesired side effects. Many muscarinic agonists targeting diseases of the CNS have failed in clinical trials mainly due to gastrointestinal and cardiovascular adverse effects attributed to the activation of peripheral M2 and M3 receptors.

[0007] Compounds that exhibit selectivity for the M4 receptor relative to the M2 and M3 receptor subtypes have been reported in WO2015118342 and WO2024028458, the disclosures of the publications are incorporated herein by reference in their entirety.

[0008] Dysregulation of dopaminergic systems is integral to several central nervous system (CNS) disorders, including neurological and psychiatric diseases and disorders. These neurological and psychiatric diseases and disorders include hyperkinetic movement disorders, and conditions, such as schizophrenia and mood disorders. The transporter protein vesicular monoamine transporter 2 (VMAT2) plays an important role in presynaptic dopamine release and regulates monoamine uptake from the cytoplasm to the synaptic vesicle for storage and release. Thus, vesicular monoamine transporter 2 (VMAT2) inhibitors can be useful for treating cognitive impairment, including treating cognitive symptoms associated with schizophrenia and other psychiatric disorders (e.g., psychotic disorders) and neurological disorders. Certain compounds that inhibit vesicular monoamine transporter 2 (VMAT2) have been reported in, for example, WO2008058261, WO2016127133, WO2018195121, WO2022203984, WO2024064178, WO2010044981, US20100113496, WO2011153157, WO2014120654, WO2015048370, US9550780, WO2016133989, and WO2021027792, the disclosures of the publications are incorporated herein by reference in their entirety. Despite the advances that have been made in this field, there remains a need for new therapeutic products useful for the treatment of neurological and psychiatric diseases and disorders and other related diseases or conditions described herein. The combination of the present disclosure fulfills these and other needs, as evident in reference to the following disclosure. SUMMARY The present disclosure provides pharmaceutical combinations of a muscarinic acetylcholine M4 receptor agonist, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, pharmaceutical compositions comprising such combinations, and methods of using such combinations for the treatment of neurological and psychiatric diseases and disorders and other related diseases or conditions described herein. In some embodiments, the present disclosure provides a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a method of improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use: (i) in a method of treating a neurological or psychiatric disease or disorder; (ii) in a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a use of a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for: (i) treating a neurological or psychiatric disease or disorder; (ii) treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base; wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a multi-pack for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a multi-pack for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a multi-pack for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a pharmaceutical composition for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a pharmaceutical composition for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a pharmaceutical composition for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a pharmaceutical composition for comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a combination comprising a unit dosage form of Compound A: , or a pharmaceutically acceptable salt thereof, and a separate unit dosage form of a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered with or without food. In some embodiments, the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar I disorder, Parkinson’s disease (or synucleinopathies) psychosis, obsessive-compulsive disorder, obsessive-compulsive disorder, treatment- refractory obsessive-compulsive, disorder, and autism spectrum disorder. In some embodiments, the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar I disorder, Parkinson’s disease (or synucleinopathies) psychosis, and obsessive-compulsive disorder. These and other embodiments of the invention disclosed herein will be set forth in greater detail as the patent disclosure proceeds. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 shows an exemplary manufacture process flow diagram for 10 mg cis- Compound A citrate monohydrate capsules. FIG.2 shows an exemplary manufacture process flow diagram for 20 and 30 mg cis- Compound A citrate monohydrate capsules. FIG.3 shows an exemplary manufacture process flow diagram for 10 mg and 20 mg cis-Compound A citrate monohydrate capsules. FIG.4 shows a summary of plasma pharmacokinetics after a single dose of 1.5 to 80 mg cis-Compound A. FIG.5 shows a summary of plasma pharmacokinetics after a single dose or repeated doses of cis-Compound A. FIG.6 shows the mean (±SEM) Positive and Negative Syndrome Scale (PANSS) total score by study visit (efficacy analysis set). FIG.7 shows Least Squares (LS) Mean (±SEM) change from baseline of Positive and Negative Syndrome Scale (PANSS) total score by study visit (efficacy analysis set). FIG.8 shows the mean (±SEM) Clinical Global Impression of Severity (CGI-S) Score by Study Visit (efficacy analysis set). FIG.9 shows proposed metabolite structures for Compound A. FIG.10 shows a general synthetic scheme for the preparation of (2R,3R,11bR)-3- (tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinoline-2,9-diol (Compound 1-9) utilizing intermediate (±)-1-(6-(benzyloxy)-7-methoxy-1,2,3,4- tetrahydroisoquinolin-1-yl)-3-(tert-butoxy)propan-2-one (Compound 1-4) and a resolution step of (±)-9-(benzyloxy)-3-(tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H- pyrido[2,1-a]isoquinolin-2-ol (Compound (±)-1-6) with (2S,3S)-2,3-bis(4- methylbenzoyloxy)butanedioic acid (DPTTA) to provide (2R,3R,11bR)-9-(benzyloxy)-3- (tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound 1-8) that is subsequently deprotected to provide Compound 1-9. FIG.11 shows a general synthetic scheme for the preparation of (2R,3R,11bR)-3- (tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinoline-2,9-diol (Compound 1-9) utilizing intermediates 1-(tert-butoxy)propan-2-one (Compound 1-20) and 3-(tert-butoxy)-4-(dimethylamino)butan-2-one (Compound 1-21) to give (±)-9-(benzyloxy)- 3-(tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-one (Compound (±)-1-5) that is subsequently reduced to provide (±)-9-(benzyloxy)-3-(tert- butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound (±)-1-6). A resolution step of Compound (±)-1-6 with (2S,3S)-2,3-bis(4- methylbenzoyloxy)butanedioic acid (DPTTA) is utilized to provide (2R,3R,11bR)-9- (benzyloxy)-3-(tert-butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound 1-8) that is subsequently deprotected to provide Compound 1-9. FIG.12 shows a general synthetic scheme for the preparation of (2R,3R,11bR)-3- (tert-butoxy)-8-fluoro-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinoline- 2,9-diol (Compound 2-11) utilizing intermediates 6-(benzyloxy)-5-fluoro-7-methoxy-3,4- dihydroisoquinoline (Compound 2-7) and 3-(tert-butoxy)-4-(dimethylamino)butan-2-one (Compound 2-8) to give (±)-9-(benzyloxy)-3-(tert-butoxy)-8-fluoro-10-methoxy- 1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-one (Compound 2-9). Compound 2-9 is subsequently reduced, purified by supercritical fluid chromatography (OJ-H column) to provide (2R,3R,11bR)-9-(benzyloxy)-3-(tert-butoxy)-8-fluoro-10-methoxy-1,3,4,6,7,11b- hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound 2-10) that is deprotected to give (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinoline-2,9-diol (Compound 2-11). FIG.13 shows a general synthetic scheme for the preparation of (2R,3R,11bR)-3- (tert-butoxy)-8-chloro-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinoline- 2,9-diol (Compound 3-1) utilizing (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-1,3,4,6,7,11b- hexahydro-2H-pyrido[2,1-a]isoquinoline-2,9-diol (Compound 1-9) and N-chlorosuccinimide (NCS), see EXAMPLE 6 for details; and the preparation of (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinoline-2,9-diol (Compound 3-2) utilizing (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-1,3,4,6,7,11b- hexahydro-2H-pyrido[2,1-a]isoquinoline-2,9-diol (Compound 1-9) and N-bromosuccinimide (NBS), see EXAMPLE 7 for details. FIG.14 shows a general synthetic scheme for the preparation of compounds of Formula (VI) and / or compounds of Formula (4-2) utilizing the 2,9-diol (Compound 4-1), and various alkylating agents; wherein R22and R23have the same meaning as described herein, LG1is a Leaving Group, and R22acan be H or C1-C4-alkyl optionally substituted with one or more substituents selected from: C1-C4-alkoxy, C1-C4-alkyl, C1-C4-haloalkyl, cyano, halogen, and hydroxy. It is understood that LG1can be a variety of leaving groups, such as those described herein and those known in the art. FIG.15 shows a general synthetic scheme for the preparation of compounds of Formula (VI) utilizing the 2,9-diol (Compound 4-1), and different alkylating agents; wherein R22and R23have the same meaning as described herein. FIG.16 shows a general synthetic scheme for the preparation of compounds of Formula (VI-A) and / or compounds of Formula (6-2) utilizing the (2R,3R,11bR)-2,9-diol (Compound 6-1), and various alkylating agents; wherein R22and R23have the same meaning as described herein, LG1is a Leaving Group, and R22acan be H or C1-C4-alkyl optionally substituted with one or more substituents selected from: C1-C4-alkoxy, C1-C4-alkyl, C1-C4- haloalkyl, cyano, halogen, and hydroxy. It is understood that LG1can be a variety of leaving groups, such as those described herein and those known in the art. FIG.17 shows a general synthetic scheme for the preparation of compounds of Formula (VI-A) utilizing the (2R,3R,11bR)-2,9-diol (Compound 6-1), and different alkylating agents; wherein R22and R23have the same meaning as described herein. FIG.18A and FIG.18B show 10 mg / kg Compound X (M4 agonist) had no effect on rat conditioned avoidance responding or escape failures when dosed alone but produced a leftward shift for both measures in response to Compound E (VMAT2 inhibitor). Values are expressed as means ± SEM. *: p<0.05, post-treatment (pattern-filled bars) vs. pre-treatment (open bars) by a Wilcoxon matched-pairs signed-ranks tests. FIG.19 shows 10 mg / kg Compound X (M4 agonist) and 1 mg / kg Compound Y (VMAT2 inhibitor) both produce modest, non-significant decreases in rat motor activity when dosed separately. However, the combination of the two doses demonstrated a significant decrease in locomotor activity. Values are expressed as means ± SEM. **: p<0.01, treatment vs vehicle by an unpaired t test. DETAILED DESCRIPTION Definitions In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments. However, one skilled in the art will understand that the invention may be practiced without these details. In other instances, well- known structures have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” Further, headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention. Reference throughout this specification to “one embodiment” or “an embodiment” or “some embodiments” or “a certain embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” or “in some embodiments” or “in a certain embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Also, as used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used herein, “Compound A” may be referred to as ethyl 2-[4-(1-methyl-1H- pyrazol-5-yl)-1-piperidinyl]-6-azaspiro[3.4]octane-6-carboxylate, or ethyl 2-[4-(1-methyl- 1H-pyrazol-5-yl)piperidin-1-yl]-6-azaspiro[3.4]octane-6-carboxylate and has the following chemical structure: . As used herein, “Compound A citrate monohydrate” may be referred to as: ethyl 2-[4-(1-methyl-1H-pyrazol-5-yl)-1-piperidinyl]-6-azaspiro[3.4]octane-6- carboxylate citrate monohydrate, ethyl 2-[4-(1-methyl-1H-pyrazol-5-yl)piperidin-1-yl]-6-azaspiro[3.4]octane-6- carboxylate citrate monohydrate; ethyl 2-[4-(1-methyl-1 H-pyrazol-5-yl)-1-piperidinyl]-6-azaspiro[3.4]octane-6- carboxylate, citrate (1:1), hydrate; or ethyl 2-[4-(1-methyl-1H-pyrazol-5-yl)piperidin-1-yl]-6-azaspiro[3.4]octane-6- carboxylate, citrate (1:1), hydrate. In some embodiments, the stereochemistry of “Compound A” is cis, i.e., cis- Compound A has the following chemical structure: , with a CAS Registry Number of 1803346-98-6. In some embodiments “cis-Compound A citrate monohydrate” may be referred to as: ethyl cis-2-[4-(1-methyl-1H-pyrazol-5-yl)-1-piperidinyl]-6-azaspiro[3.4]octane-6- carboxylate citrate monohydrate; ethyl cis-2-[4-(1-methyl-1H-pyrazol-5-yl)piperidin-1-yl]-6-azaspiro[3.4]octane-6- carboxylate citrate monohydrate; ethyl cis-2-[4-(1-methyl-1H-pyrazol-5-yl)piperidin-1-yl]-6-azaspiro[3.4]octane-6- carboxylate, citrate (1:1), hydrate; or ethyl cis-2-[4-(1-methyl-1H-pyrazol-5-yl)-1-piperidinyl]-6-azaspiro[3.4]octane-6- carboxylate, citrate (1:1), hydrate; and has a CAS number of 2920742-36-3. Compound A and its pharmaceutically acceptable salts thereof, including Compound A citrate monohydrate, can be prepared according to WO 2015 / 118342 and WO2024 / 028458, the disclosures of the publications are incorporated herein by reference in their entirety. Compound A and its pharmaceutically acceptable salts may form solvates, including hydrates. Solvates formed by the incorporation into the solid-state structure (e.g., crystal structure) of the compounds and salts described herein of molecules of a non-toxic pharmaceutically acceptable solvent. Examples of such solvents include water, alcohols (such as ethanol, isopropanol, and butanol) and dimethyl sulfoxide. Solvates can be prepared by recrystallizing the compounds and salts with a solvent or mixture of solvents containing the solvating solvent. Whether or not a solvate has been formed in any given instance can be determined by subjecting crystals to analysis using well known and standard techniques such as thermogravimetric analysis (TGE), differential scanning calorimetry (DSC) and X-ray crystallography. The solvates can be stoichiometric or nonstoichiometric solvates. In some embodiments, the solvate is a hydrate, such as a hemihydrate, monohydrate, or dihydrate. As used herein, “vesicular monoamine transporter 2 (VMAT2) inhibitor” or “VMAT2 inhibitor” refers to a compound that inhibits the vesicular monoamine transporter 2 receptor with a Kiof about 100nM or less in an assay known in the art, for example, one of the assays described in EXAMPLE 17. Numerous examples of a “vesicular monoamine transporter 2 (VMAT2) inhibitor” are shown herein. As used herein, “about” means ± 20% of the stated value, and includes more specifically values of ± 10%, ± 5%, ± 2% and ± 1% of the stated value. As used herein, “up-titration” of a therapeutic agent refers to increasing the amount of the agent administered to a patient at one or more instances for a specified period(s) to achieve a therapeutic effect while reducing the risk of dose-limiting intolerability that would likely otherwise occur if the agent were to be administered at the final dose at the beginning of the treatment. As used herein, the term “somnolence” refers to a feeling of drowsiness or sleepiness. The terms “somnolence”, “drowsiness”, “sleepiness”, and equivalents thereof, may be used interchangeably. As used herein, the term “sedation” refers to the depression of a subject’s awareness to the environment and reduction of his or her responsiveness to external stimulation. As used herein, the term “fatigue” refers to a state of impairment that can include physical and / or mental elements, associated with lower alertness and reduced performance. As used herein, the term “lethargy” refers to a condition marked by drowsiness and an unusual lack of energy and mental alertness. As used herein, “administering to a patient” refers to the process of introducing a composition or dosage form into the patient via an art-recognized means of introduction. As used herein, “adjusting administration”, “altering administration”, “adjusting dosing”, or “altering dosing “ are all equivalent and mean tapering off, reducing, or increasing the dose of the substance, ceasing to administer the substance to the patient, or substituting a different active agent for the substance. As used herein, “treat”, “treating”, and “treatment” are meant to include alleviating or abrogating a disorder, disease, or condition, or one or more of the symptoms associated with the disorder, disease, or condition; or alleviating or eradicating the cause(s) of the disorder, disease, or condition itself. As used herein, “adjunctive therapy” refers to a treatment that is used in conjunction with a primary treatment and its purpose is to assist the primary treatment. Adjunctive therapies are co-administered therapies. For example, if obsessive-compulsive disorder is being treated, the primary therapy may be, e.g., an antidepressant, and the co-administration of a compound described herein would be considered an adjunctive therapy. Likewise, if schizophrenia is being treated, the primary therapy may be, e.g., an antipsychotic agent. As used herein, “co-administer” and “co-administration” and variants thereof mean the administration of at least two drugs to a patient either subsequently, simultaneously, or consequently proximate in time to one another (e.g., within the same day, or week or period of 30 days, or sufficiently proximate that each of the at least two drugs can be simultaneously detected in the blood plasma). When co-administered, two or more active agents can be co- formulated as part of the same composition or administered as separate formulations. This also may be referred to herein as “concomitant” administration or variants thereof. Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Its clinical features include cognitive dysfunction, memory abnormalities, progressive impairment in activities of daily living (ADL), and a host of behavioral and neuropsychiatric symptoms. While the diagnostic criteria for AD focus mostly on the related cognitive deficits, it is the behavioral and neuropsychiatric symptoms that are most troublesome for caregivers and lead to poor quality of life for patients. These symptoms include agitation, aggressive behaviors, and psychosis. As used herein, “amelioration of the symptoms” of a particular disorder by administration of a particular pharmaceutical composition refers to any lessening, whether permanent or temporary, lasting or transient, that can be attributed to or associated with administration of the composition. As used herein, “baseline” refers to the period of time just prior to initiation of therapy. The patient's condition just prior to initiation of therapy can be referred to as the patient's baseline condition. As used herein, “bipolar I disorder” (bipolar mania) is a manic-depressive illness characterized by the occurrence of at least one manic episode and may present with or without mixed or psychotic features. Most patients also exhibit one or more depressive episodes and often have had one or more major depressive episodes. Bipolar I disorder may coexist with other disorders, such as post-traumatic stress disorder (PTSD), substance use disorders, and mood disorders. Bipolar disorder is estimated to affect 2.8% of the United States Population. As used herein, the “Clinical Global Impression – Severity” or “CGI-S” is an investigator administered, 7-point scale to assess patient’s severity of illness. See, e.g., Busner J, Targum SD. The clinical global impressions scale: applying a research tool in clinical practice. Psychiatry (Edgmont).2007;4(7):28-37. As used herein the term “disorder” is intended to be generally synonymous, and is used interchangeably with, the terms “disease”, “syndrome”, and “condition” (as in medical condition), in that all reflect an abnormal condition of the human or animal body or of one of its parts that impairs normal functioning, is typically manifested by distinguishing signs and symptoms. As used herein, a “dosage” is the prescribed administration of a specific amount, number, and frequency of doses over a specific period of time. As used herein, a “dose” means the measured quantity of an active agent to be taken at one time by a patient. In certain embodiments, wherein the active agent is not a free base, the quantity is the molar equivalent to the corresponding amount of free base. As used herein, “dosing regimen” means the dose of an active agent taken at a first time by a patient and the interval (time or symptomatic) at which any subsequent doses of the active agent are taken by the patient, such as, from about 20 to about 160 mg once daily, e.g., about 20, about 40, about 60, about 80, about 100, about 120, or about 160 mg once daily. The additional doses of the active agent can be different from the dose taken at the first time. As used herein, the term “combination” or “pharmaceutical combination” is defined herein to refer to either a fixed combination in one dosage unit form, a non-fixed combination or a kit of parts for the combined administration where, e.g., Compound A, or a pharmaceutically acceptable salt thereof, and Compound B, or a pharmaceutically acceptable salt thereof, may be administered simultaneously, independently (in either order) at the same time or separately within time intervals that allow that the combination partners to show a cooperative, e.g., synergistic, effect. As used herein “kit” or “multi-pack” refers to a package containing physically discrete unit dosage forms for dispensing. Typical unit dosage forms include, but are not limited to, a tablet or a capsule. As used herein, the term “fixed dose combination” means that the active ingredients, e.g., a Compound A and Compound B, are both administered to a patient simultaneously in the form of a single unit dosage form. As used herein, the term “non-fixed combination” means that the active ingredients, e.g., Compound A and Compound B, are both administered to a patient as separate unit dosage forms either simultaneously, concurrently, or sequentially (in either order) with no specific time limits. As used herein, “effective amount” and “therapeutically effective amount” of an agent, compound, drug, composition, or combination is an amount which is nontoxic and effective for producing some desired therapeutic effect upon administration to a subject or patient (e.g., a human subject or patient). The precise therapeutically effective amount for a subject may depend upon, e.g., the subject’s size and health, the nature and extent of the condition, the therapeutics or combination of therapeutics selected for administration, and other variables known to those of skill in the art. The effective amount for a given situation is determined by routine experimentation and is within the judgment of the clinician. As used herein, “informing” means referring to or providing published material, for example, providing an active agent with published material to a user; or presenting information orally, for example, by presentation at a seminar, conference, or other educational presentation, by conversation between a pharmaceutical sales representative and a medical care worker, or by conversation between a medical care worker and a patient; or demonstrating the intended information to a user for the purpose of comprehension. As used herein, “labeling” means all labels or other means of written, printed, graphic, electronic, verbal, or demonstrative communication that is upon a pharmaceutical product or a dosage form or accompanying such pharmaceutical product or dosage form. As used herein, the terms “manage”, “managing”, and “management” refer to preventing or slowing the progression, spread or worsening of a disease or disorder, or of one or more symptoms thereof. Often, the beneficial effects that a subject derives from a prophylactic and / or therapeutic agent do not result in a cure of the disease or disorder. In this regard, the term “managing” encompasses treating a subject who had suffered from the particular disease in an attempt to prevent or minimize the recurrence of the disease. As used herein, “a medical care worker” means a worker in the health care field who may need or utilize information regarding an active agent, including a dosage form thereof, including information on safety, efficacy, dosing, administration, or pharmacokinetics. Examples of medical care workers include physicians, pharmacists, physician's assistants, nurses, aides, caretakers (which can include family members or guardians), emergency medical workers, and veterinarians. As used herein, “Medication Guide” means an FDA-approved patient labeling for a pharmaceutical product conforming to the specifications set forth in 21 CFR 208 and other applicable regulations which contains information for patients on how to safely use a pharmaceutical product. A medication guide is scientifically accurate and is based on, and does not conflict with, the approved professional labeling for the pharmaceutical product under 21 CFR 201.57, but the language need not be identical to the sections of approved labeling to which it corresponds. A medication guide is typically available for a pharmaceutical product with special risk management information. Parkinson’s Disease (PD) is a neurodegenerative disease of the central nervous system affecting primarily the motor system. Common motor symptoms include tremors, rigidity, slowness of movement, and difficulty walking. Symptoms are progressive and, as the disease worsens, non-motor symptoms become common. These include cognitive conditions such as depression, anxiety, apathy, and dementia. The cause of PD is unknown and may involve both heritable and environmental factors. Parkinson’s Disease psychosis (PDF) is another common non-motor symptom of PD and may include visual and non-visual hallucinations and delusions. Between 20% and 40% of PD patients report experiencing hallucinations or delusions, with these symptoms being more common in more advanced cases of the disease. Hallucinations have been reported as the strongest predictor for eventual institutionalization of PD patients. As used herein, “patient” or “individual” or “subject” means a mammal, including a human, for whom or which therapy is desired, and generally refers to the recipient of the therapy. As used herein, “pharmaceutically acceptable” refers to a material that is not biologically or otherwise undesirable, i.e., the material may be incorporated into a pharmaceutical composition administered to a patient without causing any undesirable biological effects or interacting in a deleterious manner with any of the other components of the composition in which it is contained. When the term “pharmaceutically acceptable” is used to refer to a pharmaceutical carrier or excipient, it is implied that the carrier or excipient has met the required standards of toxicological and manufacturing testing or that it is included on the Inactive Ingredient Guide prepared by the U.S. Food and Drug administration. “Pharmacologically active” (or simply “active”) as in a “pharmacologically active” (or “active”) derivative or analog, refers to a derivative or analog having the same type of pharmacological activity as the parent compound and approximately equivalent in degree. As used herein, in some embodiments, “pharmaceutically acceptable salt” refers to acid addition salts with an inorganic or an organic acid. Lists of suitable salts are found in WO 87 / 05297, Johnston et al., published September 11, 1987; Remington’s Pharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton, Pa., 1985, p.1418; and J. Pharm. Sci., 66, 2 (1977), the disclosures of the publications are incorporated herein by reference in their entirety. A reference for the preparation and selection of pharmaceutical salts of the present disclosure is P. H. Stahl & C. G. Wermuth “Handbook of Pharmaceutical Salts,” Verlag Helvetica Chimica Acta, Zurich, 2002, the disclosure of the publication is incorporated herein by reference in its entirety. The organic or inorganic acids include, but are not limited to, hydrochloric, hydrobromic, sulfuric, nitric, phosphoric, sulfamic, acetic, trifluoroacetic, trichloroacetic, propionic, hexanoic, cyclopentylpropionic, glycolic, glutaric, pyruvic, lactic, malonic, succinic, sorbic, ascorbic, malic, maleic, fumaric, tartaric, citric, benzoic, 3-(4-hydroxybenzoyl)benzoic, picric, cinnamic, mandelic, phthalic, lauric, methanesulfonic, ethanesulfonic, 1,2-ethane-disulfonic, 2-hydroxyethanesulfonic, benzenesulfonic, 4-chlorobenzenesulfonic, 2-naphthalenesulfonic, 4-toluenesulfonic, camphoric, camphorsulfonic, 4-methylbicyclo[2.2.2]-oct-2-ene-1-carboxylic, glucoheptonic, 3-phenylpropionic, trimethylacetic, tert-butylacetic, lauryl sulfuric, gluconic, benzoic, glutamic, hydroxynaphthoic, salicylic, stearic, cyclohexylsulfamic, quinic, muconic acid, and the like. In some embodiments, “pharmaceutically acceptable salt” refers to base addition salts with an inorganic or an organic base. Inorganic bases which may be used to prepare salts include, for example, sodium, potassium, lithium, ammonium, calcium, magnesium, iron, zinc, manganese, aluminum hydroxides, carbonates, bicarbonates, phosphates, and the like; particularly preferred are the ammonium, potassium, sodium, calcium, and magnesium hydroxides, carbonates, bicarbonates, or phosphates. Organic bases from which may be used to prepare salts include, for example, primary, secondary, and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines, basic ion exchange resins, and the like, specifically such as isopropylamine, trimethylamine, diethylamine, triethylamine, tripropylamine, and ethanolamine. As used herein, the “Positive and Negative Symptoms Scale” or “PANSS” is a reliable, well known, widely used, clinician administered, validated, 30-item scale designed to evaluate the severity of various symptoms of schizophrenia and is commonly employed in clinical studies involving antipsychotics. The subscales of the PANSS and the 5-factor model of the PANSS are commonly employed to assess different symptom domains of schizophrenia. The PANSS Positive Symptom Factor Score (PSFS) is broadly used in clinical studies of schizophrenia and has demonstrated both good test-retest reliability and validity for positive symptom assessment in patients. See, e.g., Lehman AF, Lieberman JA, Dixon LB, et al. Practice guideline for the treatment of patients with schizophrenia, second edition. Am. J. Psychiatry.2004 Feb;161(2 Suppl):1-56 and Marder SR, Davis JM, and Chouinard G. The effects of risperidone on the five dimensions of schizophrenia derived from factor analysis: combined results of the North American trials. J. Clin. Psychiatry.1997 Dec;58(12):538-46. As used herein, “prevent”, “preventing”, and “prevention” are meant to include a method of delaying and / or precluding the onset of a disorder, disease, or condition, and / or its attendant symptoms; barring a subject from acquiring a disorder, disease, or condition; or reducing a subject's risk of acquiring a disorder, disease, or condition. As used herein, a “product” or “pharmaceutical product” means a dosage form of an active agent plus published material, and optionally packaging. As used herein, “product insert” means the professional labeling (prescribing information) for a pharmaceutical product, a patient package insert for the pharmaceutical product, or a medication guide for the pharmaceutical product. As used herein, “professional labeling” or “prescribing information” means the official description of a pharmaceutical product approved by a regulatory agency (e.g., FDA or EMEA) regulating marketing of the pharmaceutical product, which includes a summary of the essential scientific information needed for the safe and effective use of the drug, such as, for example indication and usage; dosage and administration; who should take it; adverse events (side effects); instructions for use in special populations (pregnant women, children, geriatric, etc.); safety information for the patient, and the like. As used herein, “published material” means a medium providing information, including printed, audio, visual, or electronic medium, for example a flyer, an advertisement, a product insert, printed labeling, an internet web site, an internet web page, an internet pop- up window, a radio or television broadcast, a compact disk, a DVD, an audio recording, or other recording or electronic medium. As used herein, the term “schizophrenia or schizoaffective disorder” includes, but is not limited to, illnesses that describe abnormal social behavior and failure to understand what is real. Schizophrenia is described in terms of positive and negative (or deficit) symptoms. Positive symptoms are those that most individuals do not normally experience, but are present in people with schizophrenia. Negative symptoms are deficits of normal emotional responses or of other thought processes. Schizoaffective disorder causes people to experience both schizophrenia and a mood disorder at the same time. It manifests as a combination of schizophrenia symptoms, such as hallucinations and delusions, and mood disorder symptoms, such as depression, mania and / or hypomania. Methods of Treatment Provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a method of improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Provided is a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use: (i) in a method of treating a neurological or psychiatric disease or disorder; (ii) in a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is use of a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for: (i) treating a neurological or psychiatric disease or disorder; (ii) treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base; wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a multi-pack for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a multi-pack for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a multi-pack for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Provided is a pharmaceutical composition for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a pharmaceutical composition for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. Also provided is a pharmaceutical composition for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered with or without food. Indications In some embodiments, the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar disorder, Parkinson’s disease (or synucleinopathies) psychosis, obsessive-compulsive disorder, obsessive-compulsive disorder, treatment- refractory obsessive-compulsive, disorder, and autism spectrum disorder. In some embodiments, the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar disorder, Parkinson’s disease (or synucleinopathies) psychosis, and obsessive compulsive disorder. In some embodiments, the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, and psychosis. In some embodiments, the neurological or psychiatric disease or disorder is psychosis. In some embodiments, the neurological or psychiatric disease or disorder is Alzheimer’s disease psychosis. In some embodiments, the neurological or psychiatric disease or disorder is Parkinson’s disease psychosis. In some embodiments, the neurological or psychiatric disease or disorder is bipolar disorder. In some embodiments, the neurological or psychiatric disease or disorder is bipolar I disorder. In some embodiments, the neurological or psychiatric disease or disorder is schizophrenia or schizoaffective disorder. In some embodiments, the neurological or psychiatric disease or disorder is schizophrenia. In some embodiments, the neurological or psychiatric disease or disorder is schizoaffective disorder. In some embodiments, the subject has at least one sign or symptom of schizophrenia. In some embodiments, the subject has at least one positive, negative, and / or cognitive sign or symptom of schizophrenia. In some embodiments, the at least one sign or symptom is delusions, hallucinations, disorganized speech, disorganized behavior or attention, anhedonia, catatonic behavior, affective flattening, alogia, avolition, conceptual disorganization, or any combination thereof. In some embodiments, the subject is also being administered at least one co- therapeutic agent for the treatment of schizophrenia and the neurological or psychiatric disease or disorder is adjunctive treatment of schizophrenia (ATS). In some embodiments, the subject has a stable background antipsychotic medication dose. In some embodiments, the subject is residually symptomatic or has at least one residual sign or symptom after first- or second-line treatment of schizophrenia. In some embodiments, the subject is residually symptomatic or has at least one residual sign or symptom after mono- or combination therapy for schizophrenia. In some embodiments, the mono- or combination therapy is initial therapy. In some embodiments, the at least one co-therapeutic agent is at least one antipsychotic agent. In some embodiments, the antipsychotic agent is a typical antipsychotic agent. In some embodiments, the typical antipsychotic agent is benperidol, chlorpromazine, droperidol, flupentixol, fluphenazine, haloperidol, levomepromazine, loxapine, molindone, pericyazine, perphenazine, pimozide, prochlorperazine, promazine, sulpiride, thiothixene, trifluoperazine, thioridazine, zuclopenthixol, or any combination thereof. In some embodiments, the antipsychotic agent is an atypical antipsychotic agent. In some embodiments, the atypical antipsychotic agent is clozapine, olanzapine, risperidone, sertindole, quetiapine, paliperidone, asenapine, ziprasidone, surmontil, iloperidone, aripiprazole, or any combination thereof. In some embodiments, with respect to the method, the compound, or the use, before administration of Compound A, or a pharmaceutically acceptable salt thereof, either the subject or a medical care worker is informed that the administration may result in an adverse reaction selected from somnolence, sedation, fatigue, and lethargy. In a further embodiment, the adverse reaction is somnolence. In some embodiments, the subject does not perform activities requiring mental alertness such as operating a motor vehicle or operating hazardous machinery until they know how they will be affected by Compound A or a pharmaceutically acceptable salt thereof. In some embodiments, the method, the compound, or the use further comprises informing the subject or medical care worker that the subject should not perform activities requiring mental alertness. In some embodiments, the method, the compound, or the use further comprises informing the subject or medical care worker that the administration may impair judgment, thinking, or motor skills. In some embodiments, the method, the compound, or the use further comprises informing the subject or medical care worker that the administration may impair the subject’s ability to perform tasks that require complex motor and mental skills. In some embodiments, the method, the compound, or the use further comprises informing the subject or medical care worker that the administration may cause slow reaction times. In some embodiments, the method, the compound, or the use further comprises informing the subject or medical care worker that the administration may impair the subject’s ability to drive or operate hazardous machinery. In some embodiments, the method, the compound, or the use further comprises cautioning the subject about operating hazardous machinery. Methods of Dosing In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10, about 15, about 20 mg, about 25 mg, or about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the dosing regimen does not include any titration period. In some embodiments, the subject is assessed for one or more adverse events during the QD dosing. The one or more adverse events may be selected from blood pressure, heart rate, and 12-lead ECGs. In some embodiments, the QD dosing may last at least 5 weeks in the absence of one or more adverse events. In some embodiments, any method or use described herein comprises the steps: a) administering to the subject Compound A, or a pharmaceutically acceptable salt, and b) informing the subject or a medical care worker that the administration may result in an adverse reaction chosen from somnolence, sedation, fatigue, and lethargy. In some embodiments, any method or use described herein comprises the steps: a) administering to the subject Compound A, or a pharmaceutically acceptable salt, and b) monitoring an adverse reaction chosen from somnolence, sedation, fatigue, and lethargy in the subject. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose of Compound A, or a pharmaceutical acceptable salt thereof, that is administered is reduced. In some embodiments, the subject is monitored for an adverse reaction chosen from somnolence, sedation, fatigue, and lethargy in the subject. In some embodiments, the adverse reaction is somnolence. In some embodiments, the adverse reaction is sedation. In some embodiments, the adverse reaction is fatigue. In some embodiments, the adverse reaction is lethargy. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose is reduced from an amount equivalent to about 30 mg of Compound A free base to an amount equivalent to about 20 mg of Compound A free base. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose is reduced from an amount equivalent to about 30 mg of Compound A free base to an amount equivalent to about 15 mg of Compound A free base. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose is reduced from an amount equivalent to about 30 mg of Compound A free base to an amount equivalent to about 10 mg of Compound A free base. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose is reduced from an amount equivalent to about 20 mg of Compound A free base to an amount equivalent to about 15 mg of Compound A free base. In some embodiments, if the subject experiences an adverse reaction selected from somnolence, sedation, fatigue, and lethargy, the daily dose is reduced from an amount equivalent to about 20 mg of Compound A free base to an amount equivalent to about 10 mg of Compound A free base. In some embodiments, the dosing regimen comprises once a day (QD) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the dosing regimen comprises once a day (QD) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the dosing regimen does not include any titration period. In some embodiments, the subject is assessed for one or more adverse events during the QD dosing. The one or more adverse events may be selected from blood pressure, heart rate, and 12-lead ECGs. In some embodiments, the QD dosing may last at least 5 weeks in the absence of one or more adverse events. In some embodiments, the dosing regimen comprises two times a day (BID) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the dosing regimen comprises two times a day (BID) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base. In some embodiments, the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the dosing regimen does not include any titration period. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, during the titration period, at an initial daily dose equivalent to from about 10% to about 70% of the final daily dose in the final dose period, and then administration of Compound A, or a pharmaceutically acceptable salt thereof, at the final daily dose. In some embodiments, the initial daily dose in the titration period is equivalent to from about 20% to about 60% of the final daily dose. In some embodiments, the initial daily dose in the titration period is equivalent to about 25% or about 50% of the final daily dose. In some embodiments, the initial daily dose in the titration period is equivalent to about 25% of the final daily dose. In some embodiments, the initial daily dose in the titration period is equivalent to about 50% of the final daily dose. In some embodiments, the initial daily dose in the titration period is about 2.5 mg, about 5 mg, about 7.5 mg, about 10 mg, about 12.5 mg, about 15 mg, about 17.5 mg, or about 20 mg of Compound A free base. In some embodiments, the initial daily dose in the titration period is about 2.5 mg, about 5 mg, about 7.5 mg, or about 10 mg of Compound A free base. In some embodiments, the initial daily dose in the titration period is about 2.5 mg of Compound A free base. In some embodiments, the initial daily dose in the titration period is about 5 mg of Compound A free base. In some embodiments, the initial daily dose in the titration period is about 7.5 mg of Compound A free base. In some embodiments, the initial daily dose in the titration period is about 10 mg of Compound A free base. In some embodiments, the final daily dose is from about 5 mg to about 70 mg of Compound A free base. In some embodiments, the final daily dose is from about 5 mg to about 40 mg of Compound A free base. In some embodiments, the final daily dose is from about 7 mg to about 30 mg of Compound A free base. In some embodiments, the final daily dose is from about 8 mg to about 25 mg of Compound A free base. In some embodiments, the final daily dose is about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base. In some embodiments, the final daily dose is about 10 mg of Compound A free base. In some embodiments, the final daily dose is about 15 mg of Compound A free base. In some embodiments, the final daily dose is about 20 mg of Compound A free base. In some embodiments, the final daily dose is about 25 mg of Compound A free base. In some embodiments, the final daily dose is about 30 mg of Compound A free base. In some embodiments, the initial daily dose is administered QD. In some embodiments, the initial daily dose is administered BID. In some embodiments, the final daily dose is administered QD. In some embodiments, the final daily dose is administered BID. In some embodiments, the initial daily dose and final daily dose are administered QD. In some embodiments, the titration period is from about 2 to about 14 days. In some embodiments, the titration period is from about 2 to about 7 days. In some embodiments, the titration period is from about 3 to about 7 days. In some embodiments, the titration period is about 2, about 3, about 4, about 5, about 6, or about 7 days. In some embodiments, the titration period is about 2 days. In some embodiments, the titration period is about 3 days. In some embodiments, the titration period is about 4 days. In some embodiments, the titration period is about 5 days. In some embodiments, the titration period is about 6 days. In some embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is about 10 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is about 15 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is 20 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is 25 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is about 15 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is about 20 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is about 25 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is about 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 20 mg of Compound A free base, wherein the final daily dose in the final dose period is about 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days. In some further embodiments, the titration period is about 3 days. In some other further embodiments, the titration period is about 4 days. In some other further embodiments, the titration period is about 5 days. In some other further embodiments, the titration period is about 6 days. In some other further embodiments, the titration period is about 7 days. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered QD. In some other embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered BID. In some embodiments, the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose, during a first titration period, administration of an increased daily dose during a second titration period, and administration at a final daily dose in a final dose period. In some embodiments, the first titration period is from about 2 to about 14 days. In some embodiments, the first titration period is from about 2 to about 7 days. In some embodiments, the first titration period is about 2, about 3, about 4, about 5, about 6, or about 7 days. In some embodiments, the second titration period is from about 1 to about 7 days. In some embodiments, the first titration period is about 1, about 2, about 3, about 4, about 5, about 6, or about 7 days. In some embodiments, the first and second titration period combined is about 14 days. In some further embodiments, the first titration period is about 2 days, and the second titration period is about 12 days. In some further embodiments, the first titration period is about 3 days, and the second titration period is about 11 days. In some further embodiments, the first titration period is about 4 days, and the second titration period is about 10 days. In some further embodiments, the first titration period is about 5 days, and the second titration period is about 9 days. In some further embodiments, the first titration period is about 6 days, and the second titration period is about 8 days. In some further embodiments, the first titration period is about 7 days, and the second titration period is about 7 days. In some embodiments, the initial daily dose is an amount equivalent to from about 10% to about 30% of the final daily dose. In some embodiments, the initial daily dose is an amount equivalent to about 10% of the final daily dose. In some embodiments, the initial daily dose is an amount equivalent to about 15% of the final daily dose. In some embodiments, the initial daily dosage is an amount equivalent to about 20% of the final daily dose. In some embodiments, the initial daily dose is an amount equivalent to about 25% of the final daily dose. In some embodiments, the initial daily dosage is an amount equivalent to about 30% of the final daily dosage. In some embodiments, the dosages are administered BID. In some other embodiments, the dosages are administered QD. In some embodiments, the initial daily dose is an amount equivalent to from about 2.5 mg to about 10 mg of Compound A free base. In some embodiments, the initial daily dose is an amount equivalent to about 2.5 mg of Compound A free base. In some embodiments, the initial daily dose is an amount equivalent to about 5 mg of Compound A free base. In some embodiments, the initial daily dose is an amount equivalent to about 7.5 mg of Compound A free base. In some embodiments, the initial daily dose is an amount equivalent to about 10 mg of Compound A free base. In some embodiments, the dosages are administered BID. In some other embodiments, the dosages are administered QD. In some embodiments, the increased daily dose is an amount equivalent to from about 20% to about 60% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 20% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 25% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 30% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 35% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 40% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 45% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 50% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 55% of the final daily dose. In some embodiments, the increased daily dose is an amount equivalent to about 60% of the final daily dose. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the increased daily dose is an amount equivalent to from about 5 mg to about 20 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 5 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 7.5 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 10 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 12.5 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 15 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 17.5 mg of Compound A free base. In some embodiments, the increased daily dose is an amount equivalent to about 20 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the final daily dose is equivalent to from about 10 mg to about 70 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to from about 10 mg to about 40 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to from about 7 mg to about 30 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to from about 8 mg to about 25 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to about 10, about 15, about 20, about 25, or about 30 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to about 20 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to about 25 mg of Compound A free base. In some embodiments, the final daily dose is equivalent to about 30 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 15 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 20 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg of Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 25 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 15 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 20 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 15 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 20 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. In some embodiments, the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 25 mg of Compound A free base, for a second titration period of from about 1 to about 7 days, and administration at a final daily dose equivalent to about 30 mg of Compound A free base. In some embodiments, the doses are administered BID. In some other embodiments, the doses are administered QD. Also provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a method of improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a dosing regimen of a compound having the structure: , or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; for use: (i) in a method of treating a neurological or psychiatric disease or disorder; (ii) in a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) in improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, comprising: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a use of a compound having the structure of: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; in the manufacture of a medicament for: (i) treating a neurological or psychiatric disease or disorder; (ii) treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, comprising: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a compound for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a compound for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure: , or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof; wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, in combination with a compound having the structure: or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, in combination with a compound having the structure: , or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, in combination with a compound having the structure: , or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a multi-pack for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a multi-pack for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a multi-pack for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a pharmaceutical composition for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a pharmaceutical composition for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base; monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present; wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. Also provided is a pharmaceutical composition for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises: administering to the subject a dosing regimen of cis-Compound A, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, or a pharmaceutically acceptable salt thereof, in a first period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base, monitoring one or more adverse events; and administering cis-Compound A, or a pharmaceutically acceptable salt thereof, in a second period at a daily dose equivalent to from about 5 mg to about 15 mg of cis- Compound A free base if at least one of the one or more adverse events is present, wherein the one or more adverse events is selected from heart rate >110 bpm continuously for >5 hours with associated symptoms of tachycardia, and heart rate ≥40% above baseline and >100 bpm continuously for >5 hours regardless of associated symptomatology. In some embodiments, the first period is from about 1 to about 3 weeks. In some embodiments, the first period is about 1 week. In some embodiments, the first period is about 2 weeks. In some embodiments, the first period is about 3 weeks. In some embodiments, the second period is from about 1 to about 6 weeks. In some embodiments, the second period is about 1 week. In some embodiments, the second period is about 2 weeks. In some embodiments, the second period is about 3 weeks. In some embodiments, the second period is about 4 weeks. In some embodiments, the second period is about 5 weeks. In some embodiments, the second period is about 6 weeks. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 10 mg of cis- Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 15 mg of cis-Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 20 mg of cis-Compound A free base. In some embodiments, cis- Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 25 mg of cis-Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 30 mg of cis-Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the second period at a daily dose equivalent to about 5 mg of cis- Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the second period at a daily dose equivalent to about 10 mg of cis-Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the second period at a daily dose equivalent to about 15 mg of cis-Compound A free base. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered in the first period at a daily dose equivalent to about 20 mg of cis- Compound A free base and in the second period at a daily dose equivalent to about 10 mg of cis-Compound A free base. In some embodiments, the method, compound, or use comprises administering cis- Compound A, or a pharmaceutically acceptable salt thereof, in a third period at a daily dose equivalent to from about 10 mg to about 30 mg of cis-Compound A free base. In some further embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered at the same daily dose as the dose in the first period. In some further embodiments, the same daily dose is a dose equivalent to about 20 mg of cis-Compound A free base. In some embodiments, the neurological or psychiatric disease or disorder is schizophrenia. In some embodiments, the neurological or psychiatric disease or disorder is bipolar I disorder. In some embodiments, the neurological or psychiatric disease or disorder is Alzheimer’s disease psychosis. In some embodiments, the neurological or psychiatric disease or disorder is Parkinson’s disease psychosis. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate. In some further embodiments, cis- Compound A citrate monohydrate is crystalline. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered orally. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered QD. In some embodiments, the baseline assessment of the heart rate is the heart rate recorded at 30 minutes (±20 minutes) predose on Day 1. Also provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 10 mg to about 30 mg cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject a compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is use of a compound in the manufacture of a medicament for treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 10 mg to about 30 mg cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is use of a compound in the manufacture of a medicament for treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is use of a compound in the manufacture of a medicament for treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is use of a compound in the manufacture of a medicament for treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 10 mg to about 30 mg cis-Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. Also provided is a compound for use in a method for treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising: administering to the subject the compound having the structure: or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg cis- Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof. In some embodiments, the neurological or psychiatric disease or disorder is schizophrenia. In some further embodiments, the method treats positive symptoms. In some further embodiments, the method treats negative symptoms In some embodiments, the neurological or psychiatric disease or disorder is bipolar I disorder. In some embodiments, the neurological or psychiatric disease or disorder is Alzheimer’s disease. In some further embodiments, the neurological or psychiatric disease or disorder is Alzheimer’s disease psychosis. In some embodiments, the neurological or psychiatric disease or disorder is Parkinson’s disease. In some further embodiments, the neurological or psychiatric disease or disorder is Parkinson’s disease psychosis. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate. In some further embodiments, cis- Compound A citrate monohydrate is crystalline. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered orally. In some embodiments, cis-Compound A, or a pharmaceutically acceptable salt thereof, is administered QD. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered with or without food. In some embodiments, administration Compound A, or a pharmaceutically acceptable salt thereof, results in no significant food effect. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered to a subject who is in a fed or fasted state. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered with food. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is administered without food. Pharmaceutical Compositions, Combinations, Multi-Packs In some embodiments, the present disclosure provides a pharmaceutical composition for comprising a compound having the structure: , or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a combination comprising a unit dosage form of Compound A: , or a pharmaceutically acceptable salt thereof, and a separate unit dosage form of a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. In some embodiments, the present disclosure provides a multi-pack comprising a unit dosage form of Compound A: , or a pharmaceutically acceptable salt thereof, and a discrete unit dosage form of a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base. It is understood that the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, can be selected from any of the VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described herein, (see VMAT2 Inhibitors section). It is understood that representative dosages for the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, can be selected from any of the dosages described herein, (see VMAT2 Inhibitors section). In some embodiments, the dosage is based on the weight of the free base of the VMAT2 Inhibitor. In some embodiments, the unit dosage forms are administered simultaneously. In some embodiments, the unit dosage forms are administered separately. In some embodiments, the unit dosage forms are administered sequentially. Compounds In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is Compound A free base. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of Compound A. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of Compound A. In some embodiments, the citrate salt of Compound A is crystalline. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is Compound A citrate monohydrate, wherein the molar ratio between Compound A, citric acid, and water is about 1:1:1. In some embodiments, the Compound A citrate monohydrate is crystalline. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A free base. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of cis-Compound A. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis-Compound A. In some embodiments, the citrate salt of cis-Compound A is crystalline. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:1. In some embodiments, the cis-Compound A citrate monohydrate is crystalline. In some embodiments, the crystalline form of the citrate salt of Compound A, Compound A citrate monohydrate, or cis-Compound A citrate monohydrate is characterized by at least one XRPD peak, in terms of 2-theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°. In some embodiments, the crystalline form of cis- Compound A citrate monohydrate is characterized by at least two XRPD peaks, in terms of 2-theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°. In some embodiments, the crystalline form of cis-Compound A citrate monohydrate is characterized by at least three XRPD peaks, in terms of 2-theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°. In some embodiments, the crystalline form of cis- Compound A citrate monohydrate is characterized by four XRPD peaks, in terms of 2- theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°. VMAT2 Inhibitors (±)-Tetrabenazine ((±)-TBZ), has been used as a drug for decades. (±)-TBZ is reported as a potent, reversible inhibitor of catecholamine uptake by VMAT2 (IC50 = 3.2 nM) (see, e.g., Scherman et al., Proc. Natl. Acad. Sci. USA, (1983) 80:584-8) and is currently used in the treatment of various hyperkinetic disorders. Inhibition of VMAT2 by (±)-TBZ results in depletion of brain monoamines in vivo (see, e.g., Pettibone et al., Eur. J. Pharmacol. (1984) 102:431-6). (±)-TBZ also inhibits presynaptic and postsynaptic dopamine receptors in rat brain (see, e.g., Login et al., (1982) Ann. Neurology 12:257-62; Reches et al., J. Pharmacol. Exp. Ther. (1983) 225:515-521). (±)-TBZ exhibits extensive first pass metabolism following oral administration to humans with little or no (±)-TBZ observed in systemic circulation. The pharmacological activity of (±)-TBZ is therefore thought to be mediated primarily by active metabolites. (±)-TBZ has two chiral centers and is a racemic mixture of two stereoisomers. (±)-TBZ has been determined to be rapidly and extensively metabolized in vivo by carbonyl reductase to four metabolic stereoisomers of 3-isobutyl-9,10- dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol, also known as dihydrotetrabenazine (DHTBZ). The inhibitory constants of these four metabolites for VMAT2 have been reported, such as, in WO2008 / 058261, EXAMPLE 7, the disclosure of the publication is incorporated herein by reference in its entirety. As shown, only two of the four DHTBZ isomers ([+]-alpha-DHTBZ and [+]-beta-DHTBZ) show significant potency as inhibitors of VMAT2. Tetrabenazine ((+ / -)-cis-tetrabenazine, Nitoman®, Xenazine®, Ro 1-9569), is a racemic mixture of (3R,11bR)-1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-3-(2-methylpropyl)- 2H-benzo[a]quinolizin-2-one, and (3S,11bS)-l,3,4,6,7, 11b-hexahydro-9,10-dimethoxy-3-(2- methylpropyl)-2H-benzo[a]quinolizin-2-one. Tetrabenazine is a vesicular monoamine transporter 2 (VMAT2) inhibitor. Tetrabenazine is prescribed for the treatment of chorea associated with Huntington’s disease. In some embodiments, the present disclosure provides Compound B: , or a pharmaceutically acceptable salt thereof. In some embodiments, tetrabenazine is a free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor is tetrabenazine, or a pharmaceutically acceptable salt thereof. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 125 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 112.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 12.5 mg to about 112.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 12.5 mg, about 25 mg, about 37.5 mg, about 50 mg, about 62.5 mg, about 75 mg, about 87.5 mg, about 100 mg, or 112.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 12.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 25 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 37.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 62.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 75 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 87.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 100 mg of tetrabenazine free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 112.5 mg of tetrabenazine free base. In some embodiments, tetrabenazine is administered to the subject according to an up- titration scheme. In some embodiments, the up-titration scheme comprises administration of tetrabenazine, or a pharmaceutically acceptable salt thereof, during the titration period, at a titrated daily dose equivalent to about 12.5 mg of tetrabenazine free base for a first period. In some embodiments, the first period is about 1 week. In some embodiments, after the first period, the titrated daily dose is increased at weekly intervals by an equivalent to about 12.5 mg of tetrabenazine free base until a daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is reached. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 1 mg to about 125 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 1 mg to about 112.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 12.5 mg to about 112.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 12.5 mg, about 25 mg, about 37.5 mg, about 50 mg, about 62.5 mg, about 75 mg, about 87.5 mg, about 100 mg, or 112.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 12.5 mg of tetrabenazine free base. In some embodiments, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 25 mg of tetrabenazine free base. In some embodiments, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 37.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 50 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 62.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 75 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 87.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 100 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 112.5 mg of tetrabenazine free base. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered BID. In some embodiments, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered TID. In some embodiments, if the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 37.5 mg of tetrabenazine free base or greater, then the daily dose of tetrabenazine (tetrabenazine), or a pharmaceutically acceptable salt thereof, is divided into three doses (i.e., TID) with a maximum single dose not to exceed about 25 mg. In some embodiments, the three doses are administered substantially 8 hours apart. Doses of 37.5 mg and up to 50 mg per day should be administered in three divided doses per day with a maximum recommended single dose not to exceed 25 mg. In some embodiments, patients requiring daily doses above 50 mg should be genotyped for the drug metabolizing enzyme CYP2D6 to determine if the patient is a poor metabolizer (PM) or an extensive metabolizer (EM) (2.2, 5.3) Maximum daily dose in PMs: 50 mg with a maximum single dose of 25 mg. Maximum daily dose in EMs and intermediate metabolizers (IMs): 100 mg with a maximum single dose of 37.5 mg. In some embodiments, tetrabenazine is a free base. In some embodiments, tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered orally. Section I: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2008058261, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (I): , or a pharmaceutically acceptable salt thereof, wherein: R1is: a) -C(=O)-O-alkyl; or b) -C(=O)-C1-C6-alkanediyl-NH2, wherein said C1-C6-alkanediyl is optionally substituted with a group selected from: -NH-C(=NH)NH2, -CO2H, -CO2Me, -SH, -C(O)NH2, -NH2, -SCH3, phenyl, -OH, 4- hydroxy-phenyl, imidazolyl, and indolyl. In some embodiments, the present disclosure provides a compound having Formula (I-A): , or a pharmaceutically acceptable salt thereof, wherein R1has the same meaning as described in Section I. In some embodiments, the present disclosure provides a compound having Formula (I-B): , or a pharmaceutically acceptable salt thereof, wherein R1has the same meaning as described in Section I. In some embodiments, the present disclosure provides a compound having Formula (I-C): , or a pharmaceutically acceptable salt thereof, wherein R1has the same meaning as described in Section I. In some embodiments, the present disclosure provides a compound having Formula (I-D): , or a pharmaceutically acceptable salt thereof, wherein R1has the same meaning as described in Section I. In some embodiments, R1is -C(=O)O-alkyl. In some embodiments, R1is -C(=O)-C1-C6-alkanediyl-NH2. In some embodiments, R1is 1-amino-2-methyl-propan-1-yl. In some embodiments, R1is (S)-1-amino-2-methyl-propan-1-yl. In some embodiments, the present disclosure provides Compound C (may be referred to as: L-Valine, (2R,3R,11bR)-1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-3-(2-methylpropyl)- 2H-benzo[a]quinolizin-2-yl ester, valbenazine, or Ingrezza®), or a pharmaceutically acceptable salt thereof: , with a CAS Registry Number of 1025504-45-3. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound C (valbenazine), or a pharmaceutically acceptable salt thereof. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 100 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 10 mg to about 100 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg, or about 100 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, or about 80 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 20 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 30 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 40 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 60 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 70 mg of Compound C free base. In some embodiments, Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 80 mg of Compound C free base. In some embodiments, the present disclosure provides L-valine (2R,3R,11bR)- 1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-3-(2-methylpropyl)-2H-benzo[a]quinolizin-2-yl ester, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound C-Tosylate, L- Valine, (2R,3R,11bR)-1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-3-(2-methylpropyl)-2H- benzo[a]quinolizin-2-yl ester, 4-methylbenzenesulfonate (1:2) salt (may be referred to as: NBI98854 tosylate, valbenazine tosylate, or valbenazine ditosylate) with the following structure: , with a CAS Registry Number of 1639208-54-0. In some embodiments, the present disclosure provides Compound C-Tosylate which has an X-ray powder diffraction pattern comprising peaks at 6.3, 17.9, and 19.7 degrees two- theta ± 0.2 theta. In some embodiments, the present disclosure provides Compound C-Tosylate which has a differential scanning calorimetry thermogram comprising an endothermic event with an onset temperature of 240 °C and a peak at 243 °C. In some embodiments, the present disclosure provides Compound C-Tosylate which has an X-ray powder diffraction pattern comprising peaks at 6.3, 17.9, and 19.7 degrees two- theta ± 0.2 theta and a differential scanning calorimetry thermogram comprising an endothermic event with an onset temperature of 240 °C and a peak at 243 °C. In some embodiments, the present disclosure provides Compound C-Tosylate which has a thermal gravimetric analysis plot comprising a mass loss of less than 0.4% when heated from 25 °C to 140 °C. In some embodiments, the present disclosure provides Compound C-Tosylate which is stable upon exposure to 25 °C and 60% relative humidity for 3 months. In some embodiments, the present disclosure provides Compound C-Tosylate which exhibits a mass increase of 1% when subjected to an increase in relative humidity from 0% to 95% relative humidity. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2008058261. In some embodiments, the compound in Section I is a free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section I, or a pharmaceutically acceptable salt thereof, is administered orally. For clarity, the definitions for the groups present in Section I used in the description of the compounds of Formula (I), and genera related thereto, have the same definitions as found in WO2008058261. Methods for synthesizing L-Valine, (2R,3R,11bR)-1,3,4,6,7,11b-hexahydro-9,10- dimethoxy-3-(2-methylpropyl)-2H-benzo[a]quinolizin-2-yl ester (alternative chemical names: (2R,3R,11bR)-3-isobutyl-9,10-dimethoxy-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1- a]isoquinolin-2-yl (S)-2-amino-3-methylbutanoate, (S)-(2R,3R,11bR)-3-isobutyl-9,10- dimethoxy-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,l-a]isoquinolin-2-yl 2-amino-3- methylbutanoate, valbenazine, or Ingrezza®) have been described in, for example, WO2008 / 058261, WO2017 / 112857, WO2021 / 050977, and WO2022 / 232060, the disclosures of the publications are incorporated herein by reference in their entirety. Certain salts and crystal forms for valbenazine have been described in WO2017 / 075340, and certain formulations for valbenazine have also been described in WO2019 / 060322 and WO2023 / 076568, the disclosures of the publications are incorporated herein by reference in their entirety. Section II: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2016127133, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (II): , or a pharmaceutically acceptable salt thereof, wherein: R2is: a) hydrogen; b) -P(=O)(OR3)2; c) -C(=O)alkyl, wherein alkyl is optionally substituted with R4and / or R5; d) -C(=O)heterocyclyl, wherein heterocyclyl is optionally substituted with R4and / or R5; e) -C(=O)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; f) -C(=O)N(R3)alkyl, wherein alkyl is optionally substituted with R4and / or R5; g) -C(=O)N(R3)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; h) -C(=O)Oalkyl, wherein alkyl is optionally substituted with R4and / or R5; or i) alkyl, wherein alkyl is optionally substituted with R4and / or R5; and wherein, each R3is independently hydrogen or alkyl; each R4is independently halo, haloalkyl, cyano, nitro, trimethylsilanyl, –OR7, –SR7, OC(O)R7, N(R7)2, C(O)R7, C(O)OR7, C(O)N(R7)2, N(R7)C(O)OR8, N(R7)C(O)R8, N(R7)C(=NR8)N(R9)2, N(R7)S(O)tR8(wherein t is 1 to 2), S(O)tOR7(where t is 1 to 2), S(O)pR7(where p is 0 to 2) or S(O)tN(R7)2(where t is 1 to 2), –OP(=O)(OR7)2, or when a single atom bears two R4groups such two R4groups may be taken together to form oxo; each R5is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, or when a single atom bears two R5groups such two R5groups may be taken together to form cycloalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4and / or R6; each R6is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4; and each R7, R8, and R9is independently hydrogen or alkyl. In some embodiments, R2is hydrogen, or a pharmaceutically acceptable salt thereof. In some embodiments, R2is -P(=O)(OR3)2, or a pharmaceutically acceptable salt thereof, wherein R3has the definition as defined in Section II. In some embodiments, R2is -C(=O)alkyl, or a pharmaceutically acceptable salt thereof, wherein alkyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is -C(=O)heterocyclyl, or a pharmaceutically acceptable salt thereof, wherein heterocyclyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is -C(=O)carbocyclyl, or a pharmaceutically acceptable salt thereof, wherein carbocyclyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is -C(=O)N(R3)alkyl, or a pharmaceutically acceptable salt thereof, wherein alkyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is -C(=O)N(R3)carbocyclyl, or a pharmaceutically acceptable salt thereof, wherein carbocyclyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is -C(=O)Oalkyl, or a pharmaceutically acceptable salt thereof, wherein alkyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, R2is alkyl, or a pharmaceutically acceptable salt thereof, wherein alkyl is optionally substituted with R4and / or R5; and both R4and R5have the definitions as defined in Section II. In some embodiments, the present disclosure provides a compound having Formula (II-A): , or a pharmaceutically acceptable salt thereof, wherein R2has the same meaning as described in Section II. In some embodiments, the present disclosure provides (Compound D), or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides [(2R,3S,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- yl]methanol, or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound D-HCl (may be referred to as [(2R,3S,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]methanol HCl salt) with the following structure: . In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2016127133, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section II is a free base. For clarity, the definitions for the groups present in Section II used in the description of the compounds of Formula (II), and genera related thereto, have the same definitions as found in WO2016127133, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section II, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (II) have been previously described, for example, in WO2016127133, the disclosure of the publication is incorporated herein by reference in its entirety. Section III: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2018195121, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (III): , or a pharmaceutically acceptable salt thereof, wherein: R10and R11are independently lower alkyl, lower cycloalkyl, or lower cycloalkylalkyl, wherein each lower alkyl, lower cycloalkyl, and lower cycloalkylalkyl is independently unsubstituted or substituted with one or more halo, cyano, or lower alkoxy; R12is lower alkyl; and R13is lower alkyl or lower cycloalkylalkyl. In some embodiments, R10is lower alkyl. In some embodiments, R10is C1-C6 saturated alkyl. In some embodiments, R10is unsubstituted lower alkyl. In some embodiments, R10is methyl, ethyl, n-propyl, iso-propyl, iso-butyl, neo-pentyl. In some embodiments, R10is substituted lower alkyl. In some embodiments, R10is lower alkyl substituted with halo. In some embodiments, R10is C1-C4saturated alkyl substituted with one, two, or three halo groups. In some embodiments, each of the one, two, or three halo groups is fluoro. In some embodiments, R10is fluoroalkyl. In some embodiments, R10is -(CH2)3CH2F, -(CH2)2CH2F, -CH2CH2F, -(CH2)4CF3, -(CH2)3CF3, -(CH2)2CF3, or -CH2CF3. In some embodiments, R13is cyclopropyl, cyclobutyl, or -CH2-cyclobutyl. In some embodiments, R13is iso-butyl or neo-pentyl. In some embodiments, the present disclosure provides a compound having Formula (III-A): , or a pharmaceutically acceptable salt thereof, wherein R10, R11, R12, and R13have the same definitions as described in Section III. In some embodiments, the present disclosure provides a compound having Formula (III-B): , or a pharmaceutically acceptable salt thereof, wherein R10, R12, and R13have the same definitions as described in Section III. In some embodiments, the present disclosure provides a compound having Formula (III-C): , or a pharmaceutically acceptable salt thereof, wherein R10has the same definition as described in Section III. In some embodiments, the present disclosure provides a compound having Formula (III-D): , or a pharmaceutically acceptable salt thereof, wherein R10has the same definition as described in Section III. In some embodiments, the present disclosure provides a compound having Formula (III-E): . or a pharmaceutically acceptable salt thereof, wherein R10has the same definition as described in Section III. In some embodiments, the present disclosure provides Compound E, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides (3R,11bS)-3-(2,2- dimethylpropyl)-10-methoxy-2-methyl-9-(3,3,3-trifluoropropoxy)- 1H,2H,3H,4H,6H,7H,11bH-piperazino[2,1-a]isoquinoline (Compound E), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound F, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides (3R,11bS)-3-(2,2- dimethylpropyl)-10-methoxy-2-methyl-9-(2,2,2-trifluoroethoxy)-1 ,11bH- piperazino[2,1-a]isoquinoline (Compound F), or a pharmaceutically acceptable salt thereof. In some embodiments, the pharmaceutically acceptable salt is the HCl salt. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 5 mg to about 150 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 10 mg to about 100 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, or about 80 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 20 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 30 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 40 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 60 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 70 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 80 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III is an HCl salt. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2018195121, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section III is a free base. For clarity, the definitions for the groups present in Section III used in the description of the compounds of Formula (III), and genera related thereto, have the same definitions as found in WO2018195121, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section III, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for synthesizing (3R,11bS)-3-(2,2-dimethylpropyl)-10-methoxy-2-methyl-9- (3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-piperazino[2,1-a]isoquinoline) and (3R,11bS)-3-(2,2-dimethylpropyl)-10-methoxy-2-methyl-9-(2,2,2-trifluoroethoxy)- 1H,2H,3H,4H,6H,7H,11bH-piperazino[2,1-a]isoquinoline have been described in, for example, WO2018195121 and WO2022 / 232380, the disclosures of the publications are incorporated herein by reference in their entirety. Section IV: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2022203984, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (IV): , or a pharmaceutically acceptable salt thereof, wherein: R14is R15, -(CH2)m-R16, or -(CH2)n-OR17; R15is C2-C4alkenyl, C1-C6alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R18; each R18is independently selected from the group consisting of: C1-C4alkoxy, C1- C4alkyl, C1-C4alkylamino, C1-C4alkylsulfonyl, C2-C4dialkylamino, C2-C4dialkylsulfamoyl, halogen, haloC1-C4alkoxy, haloC1-C4alkyl, haloC2-C4dialkylamino, 4-7 membered heterocyclyl, -CN, -OH, and oxo; R16is aryl, C3-C8cycloalkyl, 5-10 membered heteroaryl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R19; each R19is independently selected from the group consisting of: C1-C4alkyl, C1- C4alkylsulfonyl, C1-C4alkylsulfonyloxy, -CN, -CH2CN, halogen, haloC1-C4alkyl, haloC1- C4alkylsulfonyl, oxo, and -OH; R17is C1-C4alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R20; each R20is independently -CN or C3-C6cycloalkyl; m is 0, 1, 2, 3, or 4; and n is 1, 2, or 3. In some embodiments, the present disclosure provides a compound having Formula (IV-A): , or a pharmaceutically acceptable salt thereof, wherein R14has the same meaning as described in Section IV. In some embodiments, R14is C1-C4alkyl, unsubstituted or substituted with one, two, three, or four groups independently selected from the group consisting of: fluoro and -OH. In some embodiments, R14is C3-C8cycloalkyl. In some embodiments, R14is cyclopropyl. In some embodiments, R14is 4-6 membered heterocyclyl. In some embodiments, R14is oxetanyl. In some embodiments, R14is oxetan-3-yl. In some embodiments, R14is -(CH2)m-R16, wherein m is 0, 1, or 2, and R16is C3- C8cycloalkyl unsubstituted or substituted with one fluoro. In some embodiments, R14is - (CH2)m-R16, wherein m is 0 or 1, and R16is cyclopropyl unsubstituted or substituted with one fluoro. In some embodiments, R14is (1-fluorocyclopropyl)methyl). It is understood that the stereochemistry for the R14groups provided herein are assigned based on the R14group being bonded to the oxygen as shown in the formulae provided herein. Some embodiments include every combination of one or more compounds and pharmaceutically acceptable salts thereof selected from the following group shown in TABLE IV-A. Some embodiments include every combination of one or more compounds selected from the following group shown in TABLE IV-A. TABLE IV-A In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-10-methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-1), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9-(2,2- difluoroethoxy)-3-(2,2-dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-2), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9-(2,2- difluoropropoxy)-3-(2,2-dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-3), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9-cyclopropoxy- 3-(2,2-dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound IV-4), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-10-methoxy-9-(oxetan-3-yloxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-5), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-9-[(1-fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-6), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-9-(2-hydroxy-2-methylpropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-7), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-10-methoxy-9-[(2R)-3,3,3-trifluoro-2-hydroxypropoxy]- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound IV-8), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-10-methoxy-9-[(2S)-3,3,3-trifluoro-2-hydroxypropoxy]- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound IV-9), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9-(3,3-difluoro- 2-hydroxypropoxy)-3-(2,2-dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-10), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-9-[(2R)-2-hydroxypropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-11), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(2,2- dimethylpropyl)-9-[(2S)-2-hydroxypropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-12), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2022203984, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section IV is a free base. For clarity, the definitions for the groups present in Section IV used in the description of the compounds of Formula (IV), and genera related thereto, have the same definitions as found in WO2022203984, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section IV, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (IV) have been previously described, for example, in WO2022203984, the disclosure of the publication is incorporated herein by reference in its entirety. Section V: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2024064178, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (V): , or a pharmaceutically acceptable salt thereof, wherein: R21is selected from: C3-C7-cycloalkyl-C1-C4-alkylene, C1-C6-alkyl, C3-C7-cycloalkyl, C1-C4-alkyl-O-C2-C4-alkylene, C3-C7-cycloalkyl-O-C2-C4-alkylene, 3-7-membered- heterocyclyl, 3-7-membered-heterocyclyl-C1-C4-alkylene, C4-C8-bicycloalkyl-C1-C4- alkylene, C4-C7-cycloalkenyl, 5-11-membered-spiro-heterocyclyl, C5-C11-spiro-cycloalkyl, cubanyl-C1-C4-alkylene, and 4-8-membered-heterobicyclyl-C1-C4-alkylene; wherein each R21group is optionally substituted with one or more substituents selected from: cyano-C1-C4-alkylene, halogen, C1-C4-alkyl, C1-C4-haloalkyl, cyano, C1-C4- alkylsulfonyl, C3-C6-cycloalkyl, hydroxyl, C1-C4-alkoxy, and C2-C4-dialkylamino. In some embodiments, the present disclosure provides a compound having Formula (V-A): , or a pharmaceutically acceptable salt thereof, wherein R21has the same meaning as described in Section V. In some embodiments, R21is selected from: C1-C6-alkyl, C3-C7-cycloalkyl, and C3- C7-cycloalkyl-C1-C4-alkylene; wherein each group is optionally substituted with one or more halogen substituents. In some embodiments, R21is C3-C7-cycloalkyl-C1-C4-alkylene optionally substituted with one or two halogen substituents. In some embodiments, R21is C3-C4-cycloalkyl-C1-C4-alkylene optionally substituted with one or two halogen substituents. In some embodiments, R21is C3-C4-cycloalkyl-C1-C4- alkylene optionally substituted with one or two fluorine substituents. In some embodiments, R21is selected from: (cyclopropyl)methyl, (3,3-difluorocyclobutyl)methyl, and (2,2- difluorocyclopropyl)methyl. In some embodiments, R21is selected from: (cyclopropyl)methyl, cyclopropylmethoxy-d2, (3,3-difluorocyclobutyl)methyl, ((S)-2,2- difluorocyclopropyl)methyl, and ((R)-2,2-difluorocyclopropyl)methyl. In some embodiments, R21is (cyclopropyl)methyl. In some embodiments, R21is cyclopropylmethoxy-d2. In some embodiments, R21is (3,3-difluorocyclobutyl)methyl. In some embodiments, R21is ((S)-2,2- difluorocyclopropyl)methyl. In some embodiments, R21is ((R)-2,2- difluorocyclopropyl)methyl. In some embodiments, R21is C1-C6-alkyl optionally substituted with one, two, or three halogen substituents. In some embodiments, R21is selected from: methyl, 2,2-difluoropropyl, 2,2,2- trifluoroethyl, 3,3,3-trifluoropropyl, ethyl, 3-fluoropropyl, ethyl-d5, 2,2-difluoroethyl, 4,4,4- trifluorobutyl, and methoxy-d3. In some embodiments, R21is methyl. In some embodiments, R21is 2,2-difluoropropyl. In some embodiments, R21is 2,2,2-trifluoroethyl. In some embodiments, R21is 3,3,3-trifluoropropyl. In some embodiments, R21is ethyl. In some embodiments, R21is 3-fluoropropyl. In some embodiments, R21is ethyl-d5. In some embodiments, R21is 2,2-difluoroethyl. In some embodiments, R21is 4,4,4-trifluorobutyl. In some embodiments, R21is methoxy-d3. In some embodiments, R21is R1is C3-C7-cycloalkyl. In some embodiments, R21is cyclopropyl. It is understood that the stereochemistry for the R21groups provided herein are assigned based on the R21group being bonded to the oxygen as shown in the formulae provided herein. Some embodiments include every combination of one or more compounds and pharmaceutically acceptable salts thereof selected from the following group shown in TABLE V-A. Some embodiments include every combination of one or more compounds selected from the following group shown in TABLE V-A. TABLE V-A

[0009] In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V- 1), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(2,2-difluoropropoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin- 2-ol (Compound V-2), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 10-methoxy-9-(2,2,2-trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin- 2-ol (Compound V-3), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 10-methoxy-9-(3,3,3-trifluoropropoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-4), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-cyclopropoxy-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-5), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-((1-fluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-6), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-ethoxy-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-7), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(cyclopropylmethoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin- 2-ol (Compound V-8), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(3-fluoropropoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-9), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(ethoxy-d5)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-10), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(2,2-difluoroethoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2- ol (Compound V-11), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 10-methoxy-9-(4,4,4-trifluorobutoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin- 2-ol (Compound V-12), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-((3,3-difluorocyclobutyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-13), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(((S)-2,2-difluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H- pyrido[2,1-a]isoquinolin-2-ol (Compound V-14), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(((R)-2,2-difluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H- pyrido[2,1-a]isoquinolin-2-ol (Compound V-15), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 10-methoxy-9-(methoxy-d3)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-16), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(cyclopropylmethoxy-d2)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-17), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2024064178, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section V is a free base. For clarity, the definitions for the groups present in Section V used in the description of the compounds of Formula (V), and genera related thereto, have the same definitions as found in WO2024064178, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section V, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (V) have been previously described, for example, in WO2024064178, the disclosure of the publication is incorporated herein by reference in its entirety. Section VI: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in US Application Serial Nos. 63 / 567,664 and 63 / 761,354, and International Application Number: PCT / US2025 / 020561; each is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (VI): , or a pharmaceutically acceptable salt thereof, wherein: R22is selected from: 3-7-membered-heterocyclyl, 3-7-membered-heterocyclyl-C1-C4- alkylene, 4-8-membered-heterobicyclyl-C1-C4-alkylene, C1-C4-alkyl-O-C2-C4-alkylene, C1- C6-alkyl, C3-C7-cycloalkyl, C3-C7-cycloalkyl-C1-C4-alkylene, C3-C7-cycloalkyl-O-C2-C4- alkylene, C4-C8-bicycloalkyl-C1-C4-alkylene, and C5-C11-spiro-cycloalkyl; wherein each R22group is optionally substituted with one or more substituents selected from: C1-C4-alkoxy, C1-C4-alkyl, C1-C4-haloalkyl, cyano, halogen, and hydroxyl; and R23is halogen. In some embodiments, the present disclosure provides a compound having Formula (VI-A): , or a pharmaceutically acceptable salt thereof, wherein R22and R23have the same meaning as described in Section VI. In some embodiments, R23is F. In some embodiments, R23is Cl. In some embodiments, R23is Br. In some embodiments, R22is selected from: C1-C6-alkyl, C3-C7-cycloalkyl, and C3- C7-cycloalkyl-C1-C4-alkylene; wherein each R22group is optionally substituted with one or more substituents selected from: C1-C4-haloalkyl and halogen. In some embodiments, R22is selected from: C1-C6-alkyl, C3-C7-cycloalkyl, and C3- C7-cycloalkyl-C1-C4-alkylene; wherein each R22group is optionally substituted with one, two, or three substituents selected from: C1-C4-haloalkyl and halogen. In some embodiments, R22is selected from: (cyclobutyl)methyl, (cyclopropyl)methyl, (cyclopropyl)methyl-d2, cyclobutyl, cyclopropyl, ethyl, and propyl; wherein each R22group is optionally substituted with one, two, or three substituents selected from: fluoro and trifluoromethyl. In some embodiments, R22is selected from: (1-fluorocyclopropyl)methyl, (2,2- difluorocyclopropyl)methyl, (3,3-difluorocyclobutyl)methyl, (cyclopropyl)methyl-d2, 2,2,2- trifluoroethyl, 2,2-difluoroethyl, 2,2-difluoropropyl, 3-(trifluoromethyl)cyclobutyl, 3,3,3- trifluoropropyl, and cyclopropyl. In some embodiments, R22is selected from: (1- fluorocyclopropyl)methyl, (1s,3s)-3-(trifluoromethyl)cyclobutyl, (3,3- difluorocyclobutyl)methyl, (cyclopropyl)methyl-d2, [(1S)-2,2-difluorocyclopropyl]methyl, 2,2,2-trifluoroethyl, 2,2-difluoroethyl, 2,2-difluoropropyl, 3,3,3-trifluoropropyl, and cyclopropyl. In some embodiments, R22is selected from C1-C6-alkyl optionally substituted with one, two, or three substituents selected from halogen. In some embodiments, R22is selected from: ethyl and propyl; wherein each R1group is optionally substituted with one, two, or three substituents selected from fluoro. In some embodiments, R22is selected from: 2,2,2- trifluoroethyl, 2,2-difluoroethyl, 2,2-difluoropropyl, and 3,3,3-trifluoropropyl. In some embodiments, R22is 2,2,2-trifluoroethyl. In some embodiments, R22is 2,2-difluoroethyl. In some embodiments, R22is 2,2-difluoropropyl. In some embodiments, R22is 3,3,3- trifluoropropyl. In some embodiments, R22is selected from C3-C7-cycloalkyl optionally substituted with one substituent selected from C1-C4-haloalkyl. In some embodiments, R22is selected from: cyclobutyl and cyclopropyl; wherein each R1group is optionally substituted with one substituent selected from trifluoromethyl. In some embodiments, R22is selected from: cyclopropyl and 3-(trifluoromethyl)cyclobutyl. In some embodiments, R22is selected from: cyclopropyl and (1s,3s)-3-(trifluoromethyl)cyclobutyl. In some embodiments, R22is cyclopropyl. In some embodiments, R22is (1s,3s)-3-(trifluoromethyl)cyclobutyl. In some embodiments, R22is selected from C3-C7-cycloalkyl-C1-C4-alkylene optionally substituted with one or two, substituents selected from halogen. In some embodiments, R22is selected from: (cyclobutyl)methyl, (cyclopropyl)methyl, and (cyclopropyl)methyl-d2; wherein each R1group is optionally substituted with one or two substituents selected from fluoro. In some embodiments, R22is selected from: (1- fluorocyclopropyl)methyl, (2,2-difluorocyclopropyl)methyl, (3,3-difluorocyclobutyl)methyl, (cyclopropyl)methyl, and (cyclopropyl)methyl-d2. In some embodiments, R22is selected from: (1-fluorocyclopropyl)methyl, (3,3-difluorocyclobutyl)methyl, (cyclopropyl)methyl, (cyclopropyl)methyl-d2, and [(1S)-2,2-difluorocyclopropyl]methyl. In some embodiments, R22is (1-fluorocyclopropyl)methyl. In some embodiments, R22is (3,3- difluorocyclobutyl)methyl. In some embodiments, R22is (cyclopropyl)methyl. In some embodiments, R22is (cyclopropyl)methyl-d2(alternatively, cyclopropyl(2H2)methyl). In some embodiments, R22is [(1S)-2,2-difluorocyclopropyl]methyl. It is understood that the stereochemistry for the R22groups provided herein are assigned based on the R22group being bonded to the oxygen as shown in the formulae provided herein. Some embodiments include every combination of one or more compounds and pharmaceutically acceptable salts thereof selected from the following group shown in TABLE VI-A. TABLE VI-A

[0010] In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-[(2R)-2-fluoropropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-1), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-[(2S)-2-fluoropropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-2), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides cis-(2R,3R,11bR)-3-(tert- butoxy)-8-fluoro-9-[(2-fluorocyclopropyl)methoxy]-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-3), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(((1R,2R)-2-fluorocyclopropyl)methoxy)-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-4), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(((1S,2S)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-5), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides trans-(2R,3R,11bR)-3-(tert- butoxy)-8-fluoro-9-[(2-fluorocyclopropyl)methoxy]-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-6), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(((1R,2S)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-7), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(((1S,2R)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-8), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-{[(1R)-2,2-difluorocyclopropyl]methoxy}-8-fluoro-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-9), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-10-methoxy-9-[(1r,3r)-3-fluorocyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-10), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-{[(1S)-2,2-difluorocyclopropyl]methoxy}-8-fluoro-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol Compound VI-11), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-10-methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-12), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-10-methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-13), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(2,2-difluoropropoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-14), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(2,2-difluoroethoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-15), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9,10-dimethoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-16), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-{[1-(difluoromethyl)cyclopropyl]methoxy}-8-fluoro-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-17), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(2-fluoroethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-18), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(2H5)ethoxy-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-19), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides 2R,3R,11bR)-3-(tert-butoxy)-8- fluoro-9-[(1-fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-20), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-[(3,3-difluorocyclobutyl)methoxy]-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-21), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-10-methoxy-9-[(1r,3r)-3-(trifluoromethyl)cyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-22), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-10-methoxy-9-[(1s,3s)-3-(trifluoromethyl)cyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-23), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-[cyclopropyl(2H2)methoxy]-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-24), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-cyclopropoxy-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound VI-25), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 9-(cyclopropylmethoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-26), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-fluoro-9-(2H3)methoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound VI-27), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-9-{[1-(difluoromethyl)cyclopropyl]methoxy}-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-28), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-9-(2H5)ethoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-29), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-9-[cyclopropyl(2H2)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-30), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-9-(cyclopropylmethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-31), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-10-methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-32), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-10-methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-33), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-(tert-butoxy)- 8-chloro-9-[(1-hydroxycyclobutyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-34), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-ethoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-35), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-(3-fluoropropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-36), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-(2-fluoroethoxy)-10-methoxy-1 ,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-37), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-(2H5)ethoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-38), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-{[1-(difluoromethyl)cyclopropyl]methoxy}-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-39), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-10-methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-40), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-10-methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-41), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-(2,2-difluoropropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-42), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-(2,2-difluoroethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-43), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-9-cyclopropoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound VI-44), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-10-methoxy-9-[(2R)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-45), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-8-bromo-3-(tert- butoxy)-10-methoxy-9-[(2S)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-46), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in US Application Serial No.63 / 567,664, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section VI is a free base. For clarity, the definitions for the groups present in Section VI used in the description of the compounds of Formula (VI), and genera related thereto, and FIG.14 to FIG.17, have the same definitions as found in US Application Serial Nos.63 / 567,664 and 63 / 761,354, and International Application Number: PCT / US2025 / 020561; each is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section VI, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (VI) are described in the Examples provided herein and in US Application Serial Nos.63 / 567,664 and 63 / 761,354, and International Application Number: PCT / US2025 / 020561; each is incorporated herein by reference in its entirety. Section VII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2010044981, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (VII): , or a pharmaceutically acceptable salt thereof, wherein: A1-A27are independently selected from the group consisting of hydrogen and deuterium; and at least one of A1-A27is deuterium. In some embodiments, the present disclosure provides a compound having Formula (VII-A): , or a pharmaceutically acceptable salt thereof, wherein: A1-A6are independently selected from the group consisting of hydrogen and deuterium; and at least one of A1-A6is deuterium. In some embodiments, the present disclosure provides Compound G, with the following structure: , or a pharmaceutically acceptable salt thereof. AUSTEDO (deutetrabenazine, d6-Tetrabenazine ((+ / -)-cis-d6-tetrabenazine) is a vesicular monoamine transporter 2 (VMAT2) inhibitor for oral administration. Deutetrabenazine is a racemic mixture of (3R,11bR)-l,3,4,6,7,11b-hexahydro-9,10- di(methoxy-d3)-3-(2-methylpropyl)-2H-benzo[a]quinolizin-2-one and (3S,11bS)- l,3,4,6,7,11b-hexahydro-9,10-di(methoxy-d3)-3-(2-methylpropyl)-2H-benzo[a]quinolizin-2- one, also may be referred to the following chemical name: (RR, SS)-1,3,4,6,7,11b-hexahydro- 9, 10-di(methoxy-d3)-3-(2-methylpropyl)-2H-benzo[a]quinolizin-2-one. Deutetrabenazine is a selectively deuterium-substituted, stable, non-radioactive isotopic form of tetrabenazine in which the six hydrogen atoms on the two O-linked methyl groups have been replaced with deuterium atoms (i.e. -OCD3 rather than -OCH3 moieties). In some embodiments, the present disclosure provides Compound G, or a pharmaceutically acceptable salt thereof, as d6-tetrabenazinethat that is a racemic mixture of (R,R)-Compound G and (S,S)-Compound G (also referred to as: (RR,SS)-Compound G), or a pharmaceutically acceptable salt thereof, with the following structures: , or a pharmaceutically acceptable salt thereof. In some embodiments, each position represented as D in Compound G has deuterium enrichment of no less than about 90%. In some embodiments, each position represented as D in Compound G has deuterium enrichment of no less than about 98%. Crystalline d6-tetrabenazine In some embodiments, the present disclosure provides crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, having deuterium enrichment of no less than about 1%. In some embodiments, the present disclosure provides crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, having an X-ray diffractogram comprising peaks, in terms of 2^, at 6.5±0.2°, 12.2±0.2°, 14.4±0.2°, 22.4±0.2°, and 23.4±0.2°; or a pharmaceutically acceptable salt or hydrate thereof. In some embodiments, the present disclosure provides crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, having deuterium enrichment of no less than about 1% and an X-ray diffractogram comprising peaks, in terms of 2^, at 6.5±0.2°, 12.2±0.2°, 14.4±0.2°, 22.4±0.2°, and 23.4±0.2°; or a pharmaceutically acceptable salt or hydrate thereof. In some embodiments, the present disclosure provides crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, having an X-ray diffractogram comprising peaks, in terms of 2^, at 6.5±0.2°, 10.8±0.2°, 12.2±0.2°, 13.0±0.2°, 14.4±0.2°, 17.1±0.2°, 18.0±0.2°, 21.4±0.2°, 22.4±0.2°, and 23.4±0.2°. In some embodiments, the present disclosure provides crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, having a differential calorimetry trace comprising an endotherm between about 115° C and about 135° C. In some embodiments, the present disclosure provides crystalline d6-tetrabenazine R,SS)-Compound G) Form I, having a thermogravimetric analysis profile showing about 1.5% weight loss below about 150° C. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor is d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to from about 1 mg to about 100 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to from about 6 mg to about 60 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to from about 6 mg to about 54 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 6 mg, about 9 mg, about 12 mg, about 18 mg, about 24 mg, about 30 mg, about 36 mg, about 42 mg, or 48 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 9 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 12 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 18 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 24 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 30 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 36 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 42 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to about 48 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor is d6-tetrabenazine ((RR,SS)-Compound G) and is administered to the subject according to an up-titration scheme. In some embodiments, the up-titration scheme comprises administration of d6-tetrabenazine ((RR,SS)-Compound G), during the titration period, at a titrated daily dose equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base for a first period. In some embodiments, the first period, is about 1 week. In some embodiments, after the first period, the titrated daily dose is increased at weekly intervals by an equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base until a daily dose of d6- tetrabenazine ((RR,SS)-Compound G) is reached. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 100 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 60 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 54 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 6 mg, about 9 mg, about 12 mg, about 18 mg, about 24 mg, about 30 mg, about 36 mg, about 42 mg, or 48 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 9 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 12 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 18 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine G) is equivalent to about 24 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)- Compound G) is equivalent to about 30 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 36 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 42 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. In some embodiments, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 48 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base. The method, the VMAT2 inhibitor, or the use of any one of claims 359 to 397, the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is administered BID. In some embodiments, if the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 12 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base or greater, then the daily dose of d6-tetrabenazine ((RR,SS)-Compound G), or a pharmaceutically acceptable salt thereof, is divided into two doses (i.e., BID). In some embodiments, the two doses of d6-tetrabenazine ((RR,SS)-Compound G), or a pharmaceutically acceptable salt thereof, are substantially equal amounts. In some embodiments, the two doses are administered about 12 hours apart. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2010044981, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section VII is a free base. For clarity, the definitions for the groups present in Section VII used in the description of the compounds of Formula (VII), and genera related thereto, have the same definitions as found in WO2010044981, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section VII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (VII) have been previously described, for example, in WO2010044981, the disclosure of the publication is incorporated herein by reference in its entirety. Section VIII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in US20100113496, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (VIII): , or a pharmaceutically acceptable salt thereof, wherein: E1-E27are independently selected from the group consisting of hydrogen and deuterium; and at least one of E1-E27is deuterium. In some embodiments, the present disclosure provides a compound having Formula (VIII-A): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-B): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-C): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-D): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-E): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-F): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (VIII-G): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in US20100113496, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section VIII is a free base. For clarity, the definitions for the groups present in Section VIII used in the description of the compounds of Formula (VIII), and genera related thereto, have the same definitions as found in US20100113496, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section VIII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (VIII) have been previously described, for example, in US20100113496, the disclosure of the publication is incorporated herein by reference in its entirety. Section IX: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2011153157, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (IX): , or a pharmaceutically acceptable salt thereof, wherein: G1-G19and G21-G29are independently selected from the group consisting of hydrogen and deuterium; G20is selected from the group consisting of hydrogen, deuterium, -C(O)O-alkyl and - C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2,-CO2H, -CO2alkyl, -SH, -C(O)NH2, -NH2, phenyl, -OH, 4- hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of G1-G29is deuterium or contains deuterium. In some embodiments, the present disclosure provides a compound having Formula (IX-A): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-B): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-C): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-D): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-E): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-F): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (IX-G): , or a pharmaceutically acceptable salt thereof. In some embodiments, the stereochemistry for the compound of Formulae IX, IX-A, IX-B, IX-C, IX-D, IX-E, IX-F, and IX-G is 2R,3R,11bR. In some embodiments, the stereochemistry for the compound of Formulae IX, IX-A, IX-B, IX-C, IX-D, IX-E, IX-F, and IX-G is 2S,3R,11bR. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2011153157, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section IX is a free base. For clarity, the definitions for the groups present in Section IX used in the description of the compounds of Formula (IX), and genera related thereto, have the same definitions as found in WO2011153157, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section IX, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (IX) have been previously described, for example, in WO2011153157, the disclosure of the publication is incorporated herein by reference in its entirety. Section X: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2014120654, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (X): , or a pharmaceutically acceptable salt thereof, J1-J19and J21-J29are independently selected from the group consisting of hydrogen and deuterium; J20is selected from the group consisting of hydrogen, deuterium, -C(O)O-alkyl and - C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2, -CO2H, -C(O)2alkyl, -SH, -C(O)NH2, -NH2, phenyl, -OH, 4- hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of J1-J29is deuterium or contains deuterium. In some embodiments, the present disclosure provides a compound having Formula (X-A): , or a pharmaceutically acceptable salt thereof, wherein: J1-J19and J21-J39are independently selected from the group consisting of hydrogen and deuterium; and at least one of J1-J19and J21-J39is deuterium. In some embodiments, the present disclosure provides a compound having Formula (X-B): , or a pharmaceutically acceptable salt thereof, J20is selected from the group consisting of hydrogen, deuterium, -C(O)O-alkyl and - C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2, -CO2H, -C(O)2alkyl, -SH, -C(O)NH2, -NH2, phenyl, -OH, 4- hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium. In some embodiments, the present disclosure provides a compound having Formula (X-C): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (X-D): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a compound having Formula (X-E): , or a pharmaceutically acceptable salt thereof. In some embodiments, the stereochemistry for a compound of Formulae X, X-A, X- B, X-C, X-D, and X-E is 2R,3R,11bR, for example, the 2R,3R,11bR-stereoisomer for the compound of Formula (X-E) has the following chemical structure: , or a pharmaceutically acceptable salt thereof. In some embodiments, the stereochemistry for the compound of Formulae X, X-A, X-B, X-C, X-D, and X-E is 2S,3R,11bR, for example, the 2S,3R,11bR-stereoisomer for the compound of Formula (X-E) has the following chemical structure: , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2014120654, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section X is a free base. For clarity, the definitions for the groups present in Section X used in the description of the compounds of Formula (X), and genera related thereto, have the same definitions as found in WO2014120654, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section X, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (X) have been previously described, for example, in WO2014120654, the disclosure of the publication is incorporated herein by reference in its entirety. Section XI: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XI): , or a pharmaceutically acceptable salt thereof, wherein: L1-L29are independently selected from the group consisting of hydrogen and deuterium; and at least one of L1-L29is deuterium. In some embodiments, the present disclosure provides a compound of Formula (XI- A) ([(3R,11bR) / (3S,11bS)]-3-(2-hydroxy-2-methyl- propyl)-9,10-di(methoxy-d3)- 1,3,4,6,7,11b-hexahydro-pyrido[2,l-a]isoquinolin-2-one): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound H: , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound I: , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a mixture of Compound H, or a pharmaceutically acceptable salt thereof, and Compound I, or a pharmaceutically acceptable salt: . In some embodiments, the mixture of Compound H, or a pharmaceutically acceptable salt thereof, and Compound I, or a pharmaceutically acceptable salt, has a molar ratio of about 1:1. The racemic mixture of Compound H and Compound I (([(3R,11bR) / (3S,11bS)]-3-(2-hydroxy-2-methyl- propyl)-9,10-di(methoxy-d3)-1,3,4,6,7,11b- hexahydro-pyrido[2,l-a]isoquinolin-2-one)) can be referred to as the d6-Tetrabenazine Metabolite M4. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XI is a free base. For clarity, the definitions for the groups present in Section XI used in the description of the compounds of Formula (XI), and genera related thereto, have the same definitions as found in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XI, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XI) have been previously described, for example, in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. Section XII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XII): , or a pharmaceutically acceptable salt thereof, wherein: L30-L56are independently selected from the group consisting of hydrogen and deuterium; and at least one of L30-L56is deuterium. In some embodiments, the present disclosure provides a compound of Formula (XII- A) ((3-(2-hydroxy-9,10-di(methoxy-d3)-1,3,4,6,7,11b- hexahydro-2H-pyrido[2,1- a]isoquinolin-3-yl)-2-methyl-propionic acid)): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides a diastereomeric mixture of compounds of Formula (XII-A) (can be referred to as a diastereomeric mixture of 3-(2- hydroxy-9,10-di(methoxy-d3)-1,3,4,6,7,11b- hexahydro-2H-pyrido[2,1-a]isoquinolin-3-yl)-2- methyl-propionic acid), or a pharmaceutically acceptable salt thereof. The diastereomeric mixture of compounds of Formula (XII-A) can be referred to as the d6-Tetrabenazine Metabolite M1. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XII is a free base. For clarity, the definitions for the groups present in Section XII used in the description of the compounds of Formula (XII), and genera related thereto, have the same definitions as found in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XII) have been previously described, for example, in WO2015048370, the disclosure of the publication is incorporated herein by reference in its entirety. Section XIII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2016133989, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XIII): , or a pharmaceutically acceptable salt thereof, wherein: Q1-Q2and Q21are independently selected from the group consisting of -CH3, -CH2D; -CD2H, and -CD3; Q3-Q20are independently selected from the group consisting of hydrogen and deuterium; and at least one of Q1-Q21is deuterium or contains deuterium. In some embodiments, Q10and Q14are hydrogen. In some embodiments, Q1is CD3. In some embodiments, Q2is CD3. In some embodiments, Q21is CD3. In some embodiments, Q6and Q7are deuterium. In some embodiments, Q8and Q9are deuterium. In some embodiments, Q6-Q9are deuterium. In some embodiments, Q11and Q12are deuterium. In some embodiments, Q13is deuterium. In some embodiments, Q15and Q16are deuterium. In some embodiments, Q11, Q12, Q15, and Q16are deuterium. In some embodiments, Q11, Q12, Q13, Q15, and Q16are deuterium. In certain embodiments, Q6-Q9, Q11-Q13, and Q15, and Q16are deuterium. In some embodiments, Q11, Q12, Q15, and Q16are deuterium, Q1is CD3 and Q2is CD3. In some embodiments, Q11, Q12, Q13, Q15, and Q16are deuterium, Q1is CD3, and Q2is CD3. In some embodiments, Q11, Q12, Q13, Q15, and Q16are deuterium and Q21is CD3. In some embodiments, Q11, Q12, Q13, Q15, and Q16are deuterium, Q1is CD3, Q2is CD3, and Q21is CD3. In some embodiments, Q6-Q9are deuterium, Q1is CD3 and Q2is CD3. In some embodiments, Q6-Q9are deuterium, Q1is CD3, Q2is CD3, and Q21is CD3. In some embodiments, Q6-Q9, Q11- Q13, and Q15, and Q16are deuterium, Q1is CD3and Q2is CD3. In some embodiments, Q6-Q9, Q11- Q13, and Q15, and Q16are deuterium and Q21is CD3. In some embodiments, Q6-Q9, Q11- Q13, and Q15, and Q16are deuterium, Q1is CD3, Q2is CD3, and Q21is CD3. Also provided herein are embodiments according to each of the embodiments in Section XIII, wherein: every other substituent among Q3-Q20not specified as deuterium is hydrogen; and if any one or more of Q1-Q2and Q21is not specified to be -CD3, then it is (they are) -CH3. Bevantolol ((±)-bevantolol; DL-bevantolol; has been described as a vesicular monoamine transporter 2 (VMAT2) inhibitor; NSC 132348; 1-[[2-(3,4- dimethoxyphenyl)ethyl]amino]-3-(3-methylphenoxy)-2-propanol; the Chemical Registry Number for is 59170-23-9. In some embodiments, the present disclosure provides Compound K (Bevantolol), or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound L, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2016133989, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XIII is a free base. For clarity, the definitions for the groups present in Section XIII used in the description of the compounds of Formula (XIII), and genera related thereto, have the same definitions as found in WO2016133989, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XIII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XIII) have been previously described, for example, in WO2016133989, the disclosure of the publication is incorporated herein by reference in its entirety. Section XIV: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XIV): , or a pharmaceutically acceptable salt thereof, wherein: R24is a C2-C10fluorinated aliphatic radical; R25is a C1-C10aliphatic radical, or a C3-C10 cycloaliphatic radical; R26is hydrogen or a C1-C10 aliphatic radical; and R27is hydrogen or a C1-C10 aliphatic radical. In some embodiments, the present disclosure provides a compound having Formula (XIV-A): , or a pharmaceutically acceptable salt thereof, wherein R24, R25, R26, and R27have the same definitions as described herein in Section XIV. In some embodiments, R24is selected from C2-C6fluoroalkyl, C1-C6fluoroalkoxy(C1- C6alkyl)-, C2-C6fluorohaloalkyl, and C1-C6fluoroalkylcarbonyl(C1-C6alkyl)-; R25is selected from C1-C6alkyl and C3-C8cycloalkyl; and R26and R27are each independently selected from C1-C6alkyl and C1-C6alkoxy. In some embodiments, R24is a C2-C10fluorinated aliphatic radical; R25is isobutyl; and R26and R27are methoxy groups. In some embodiments, the present disclosure provides Compound M, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound N, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides a compound comprising19F described generically or specifically in Section XIV or disclosed in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound comprising18F described generically or specifically in Section XIV or disclosed in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XIV is a free base. For clarity, the definitions for the groups present in Section XIV used in the description of the compounds of Formula (XIV), and genera related thereto, have the same definitions as found in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XIV, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XIV) have been previously described, for example, in WO2009055520, the disclosure of the publication is incorporated herein by reference in its entirety. Section XV: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XV): , or a pharmaceutically acceptable salt thereof, wherein: R28is a C1-C10fluorinated aliphatic radical; R29is hydrogen or a C1-C10aliphatic radical; and R30is hydrogen or a C1-C10 aliphatic radical. In some embodiments, the present disclosure provides a compound having Formula (XV-A): , or a pharmaceutically acceptable salt thereof, wherein R28, R29, and R30have the same definitions as described herein in Section XV. In some embodiments, R28is a C1-C10fluorinated aliphatic radical; R29is hydrogen or a C1-C10 aliphatic radical; and R30is hydrogen or a C1-C10 aliphatic radical. In some embodiments, R28is a C5-C10 fluoroaliphatic radical and R29and R30are methoxy groups. In some embodiments, the present disclosure provides Compound O, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides a compound comprising19F described generically or specifically in Section XV or disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound comprising18F described generically or specifically in Section XV or disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XV is a free base. For clarity, the definitions for the groups present in Section XV used in the description of the compounds of Formula (XV), and genera related thereto, have the same definitions as found in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XV, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XV) have been previously described, for example, in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. Section XVI: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XVI): , or a pharmaceutically acceptable salt thereof, wherein: R31is a C1-C10 fluorinated aliphatic radical; R32is hydrogen or a C1-C10 aliphatic radical; R33is hydrogen or a C1-C10 aliphatic radical; and R34is hydrogen, a C1-C10 aliphatic radical, a C3-C10cycloaliphatic radical, or a C3-C10aromatic radical. In some embodiments, the present disclosure provides a compound having Formula (XVI-A): , or a pharmaceutically acceptable salt thereof, R31, R32, R33, and R34have the same definitions as described herein in Section XVI. In some embodiments, R31is a C5-C10 fluoroaliphatic radical, and R32and R33are methoxy groups. In some embodiments, R34is hydrogen. In some embodiments, the present disclosure provides Compound P, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound Q, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides a compound comprising19F described generically or specifically in Section XVI or disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound comprising18F described generically or specifically in Section XVI or disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XVI is a free base. For clarity, the definitions for the groups present in Section XVI used in the description of the compounds of Formula (XVI), and genera related thereto, have the same definitions as found in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XVI, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XVI) have been previously described, for example, in WO2009070552, the disclosure of the publication is incorporated herein by reference in its entirety. Section XVII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XVII): , or a pharmaceutically acceptable salt thereof, wherein: R35is a C1-C10 fluorinated aliphatic radical; R36is a C1-C10 aliphatic radical; R37is hydrogen or a C1-C10 aliphatic radical; R38is hydrogen or a C1-C10 aliphatic radical; and R39 is hydrogen, a C1-C10aliphatic radical, a C2-C10cycloaliphatic radical, or a C2-C20aromatic radical. In some embodiments, the present disclosure provides a compound having Formula (XVII-A): , or a pharmaceutically acceptable salt thereof, R35, R36, R37, R38, and R39have the same definitions as described herein in Section XVII. In some embodiments, the present disclosure provides a compound having Formula (XVII-B): , or a pharmaceutically acceptable salt thereof, R35, R36, R37, and R38have the same definitions as described herein in Section XVII. In some embodiments, R35is a C1-C10fluorinated aliphatic radical; R36is a C1-C10aliphatic radical; R37is hydrogen or a C1-C10 aliphatic radical; and R38is hydrogen or a C1- C10 aliphatic radical. In some embodiments, R35is selected from C1-C6fluoroalkyl, C2-C6fhioroalkenyl, C2- C6fluoroalkynyl C1-C6fluoroalkoxy(C1-C6alkyl), C1-C6fluorohaloalkyl, C1- C6fluorohydroxyalkyl, and C1-C6fluoroalkylcarbonyl(C1-C6alkyl), and is suitably C2- C6fluoroalkynyl; R36is selected from C1-C6alkyl and C3-C8cycloalkyl, and is suitably C1- C6alkyl; R37and R38are each independently selected from C1-C6alkyl and C1-C6alkoxy; R39is selected from hydrogen, (C1-C6alkyl)carbonyl, and phenyl. In some embodiments, -OR39is an ester moiety. In some embodiments, the present disclosure provides Compound R, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound S, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides a compound comprising19F described generically or specifically in Section XVII or disclosed in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound comprising18F described generically or specifically in Section XVII or disclosed in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XVII is a free base. For clarity, the definitions for the groups present in Section XVII used in the description of the compounds of Formula (XVII), and genera related thereto, have the same definitions as found in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XVII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XVII) have been previously described, for example, in WO2009073677, the disclosure of the publication is incorporated herein by reference in its entirety. Section XVIII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2009126305, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XVIII): , or a pharmaceutically acceptable salt thereof, wherein: R40, R41, R42, R45, and R46are independently selected from H, halogen, hydroxyl, C1- C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether; R43and R44, which are attached to one or more positions of at least one carbon atom of the respective rings, are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1- C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether; X is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle, wherein each alkyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle may be optionally substituted with at least one substituent; Y is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic, wherein each alkyl, alkenyl, alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic may be optionally substituted with at least one substituent; “---” is a single bond or a double bond; and “---” is an optional bond, when present the bond is a single bond or a double bond. In some embodiments, the present disclosure provides a compound having Formula (XVIII-A): , or a pharmaceutically acceptable salt thereof, wherein R40, R41, R42, R45aand R46aare independently selected from the group consisting of H, halogen, C1-C8alkyl, C1-C8alkenyl, and C1-C8alkynyl; R43and R44, which are attached to one or more positions of at least one carbon atom of the respective rings, are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1- C8alkenyl, C1-C8alkynyl, and C1-C8alkoxy; and “---” is an optional bond, when present the bond is a single bond or a double bond. In some embodiments, the present disclosure provides a compound having Formula (XVIII-B): , or a pharmaceutically acceptable salt thereof, wherein R40, R41, and R42are independently selected from the group consisting of H, C1-C8alkyl, C1-C8alkenyl, and C1-C8alkynyl; and “---” is an optional bond, wherein the optional bond is a single bond or a double bond. In some embodiments, the present disclosure provides a compound having Formula (XVIII-C): , or a pharmaceutically acceptable salt thereof, wherein R40, R45aand R46aare independently selected from the group consisting H, halogen, hydroxyl, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8- membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH1 NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether; X is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle, wherein each alkyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle may be optionally substituted with at least one substituent; and Y is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic, wherein each alkyl, alkenyl, alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic may be optionally substituted with at least one substituent. In some embodiments, the present disclosure provides a compound having Formula (XVIII-D): , or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides Compound T, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound U, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides Compound V, or a pharmaceutically acceptable salt thereof, with the following structure: . In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2009126305, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XVIII is a free base. For clarity, the definitions for the groups present in Section XVIII used in the description of the compounds of Formula (XVIII), and genera related thereto, have the same definitions as found in WO2009126305, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XVIII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XVIII) have been previously described, for example, in WO2009126305, the disclosure of the publication is incorporated herein by reference in its entirety. Section XIX: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in US20170304227, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XIX): , or a pharmaceutically acceptable salt thereof, wherein: “q” is an integer in the range from 1 to 3; “s” is zero or an integer from 1 to 5; R47and R48are each independently an aryl group, wherein R47and R48are each independently unsubstituted or substituted by one or more substituents selected from the group consisting of methyl; deuteromethyl (CD3); tritiomethyl (CT3); ethyl; propyl; isopropyl; C4-C7 straight chain or branched alkyl; C3-C6 cycloalkyl; C4-C7 alkenyl; benzyl; phenylethyl; amino; N-methylamino; N,N-dimethylamino; carboxylate; methylcarboxylate; ethylcarboxylate; propylcarboxylate; isopropylcarboxylate; carboxaldehyde; acetoxy; propionyloxy; isopropionyloxy; cyano; aminomethyl; N-methylaminomethyl; N,N- dimethylaminomethyl; carboxamide; N-methylcarboxamide; N,N-dimethylcarboxamide; acetyl; propionyl; formyl; benzoyl sulfate; phenyl; methylsulfate; hydroxyl; methoxy; ethoxy; propoxy; isopropoxy; thiol; methylthio; ethylthio; propiothiol; fluoro; chloro; bromo; iodo; trifluoromethyl; vinyl; allyl; propargyl; nitro; carbamoyl; ureido; azido; isocyanate; thioisocyanate; hydroxylamino; nitroso; a saturated or unsaturated hydrocarbon ring; a nitrogen-containing heterocyclic moiety; an oxygen-containing heterocyclic moiety; a sulfur- containing heterocyclic moiety; a selenium-containing heterocyclic moiety; a mixed heterocyclic moiety containing at least two atoms selected from the group consisting of nitrogen, oxygen and sulfur; and ortho, meta or para-substituted benzene; R49is methyl, ethyl, propyl, isopropyl, hydroxymethyl, 2-hydroxyethyl, 1- hyhydroxyethyl, methoxymethyl, 2-methoxyethyl, 1-methoxyethyl, aminomethyl, 2- aminoethyl, 1-aminoethyl, N-methylaminomethyl, 2-N-methylaminoethyl, 1-N- methylaminoethyl, N,N-dimethylaminomethyl, 2- N,N-dimethylaminoethyl, or 1-N,N- dimethylaminoethyl group; and R50is a hydrogen atom or a methyl, ethyl, propyl, or isopropyl group. In some embodiments, the present disclosure provides a compound having Formula (XIX-A): , or a pharmaceutically acceptable salt thereof, wherein R47, R48, R49, and R50have the same meaning as described herein in Section XIX. In some embodiments, the present disclosure provides a compound having Formula (XIX-B): , or a pharmaceutically acceptable salt thereof, wherein R47, R48, R49, and R50have the same meaning as described herein in Section XIX. In some embodiments, the present disclosure provides a compound wherein: “q”=l or 2; “s”=l, 2, 3, 4, or 5; R47=Ph, 4-BrPh, 4-MeOPh, 4-HOPh, 4-FPh, 4-NO2Ph, 4-NH2Ph, or 3,4-diMeOPh; R48=Ph, 4-MeOPh, PhO, 4-HOPh, 3,4-di-BnOPh, 3,4-di-HOPh, or 4-BrPh; R49=Me; and R50=H or CH3. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, selected from the following: 1. “q”=l, “s”=l, R47=Ph, R48=Ph, R49=Me, R50=H; 2. “q”=l, “s”=l, R47=Ph, R48=Ph, R49=Me, R50=CH3; 3. “q”=l, “s”=l, R47=4-BrPh, R48=Ph, R49=Me, R50=H; 4. “q”=l, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=H; 5. (R)-, “q”=l, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=H; 6. (S)-, “q”=l, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=H; 7. “q”=l, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=CH3; 8. “q”=l, “s”=2, R47=Ph, R48=4-MeOPh, R49=Me, R50=H; 9. (R)-, “q”=l, “s”=2, R47=Ph, R48=4-MeOPh, R49=Me, R50=H; 10. (S)-, “q”=l, “s”=2, R47=Ph, R48=4-MeOPh, R49=Me, R50=H; 11. “q”=l, “s”=2, R47=4-BrPh, R48=Ph, R49=Me, R50=H; 12. (R)-, “q”=l, “s”=2, R47=4-BrPh, R48=Ph, R49=Me, R50=H; 13. (S)-, “q”=l, “s”=2, R47=4-BrPh, R48=Ph, R49=Me, R50=H; 14. “q”=l, “s”=3, R47=4-BrPh, R48=Ph, R49=Me, R50=H; 15. “q”=l, “s”=3, R47=Ph, R48=Ph, R49=Me, R50=H; 16. “q”=l, “s”=2, R47=4-BrPh, R48=4-MeOPh, R49=Me, R50=H; 17. “q”=l, “s”=4, R47=Ph, R48=Ph, R49=Me, R50=H; 18. “q”=l, “s”=5, R47=Ph, R48=Ph, R49=Me, R50=H; 19. “q”=l “s”=l, R47=Ph, R48=PhO, R49=Me, R50=H; 20. “q”=l, “s”=l, R47=4-BrPh, R48=PhO, R49=Me, R50=H; 21. “q”=l, “s”=l, R47=Ph, R48=4-HOPh, R49=Me, R50=H; 22. “q”=l, “s”=l, R47=Ph, R48=3,4-diBnOPh, R49=Me, R50=H; 23. “q”=l, “s”=l, R47=Ph, R48=3,4-di-HOPh, R49=Me, R50=H; 40. “q”=l, “s”=2, R47=4-FPh, R48=4-MeOPh, R49=Me, R50=H; 41. “q”=l, “s”=l, R47=4-NO2Ph, R48=Ph, R49=Me, R50=H; 42. “q”=l, “s”=2, R47=4-NO2Ph, R48=Ph, R49=Me, R50=H 43. “q”=l, “s”=2, R47=4-NO2Ph, R48=4-MeOPh, R49=Me, R50=H 44. “q”=l, “s”=l, R47=4-NH2Ph, R48=Ph, R49=Me, R50=H 45. “q”=l, “s”=2, R47=4-NH2Ph, R48=Ph, R49=Me, R50=H; 46. “q”=l, “s”=2, R47=3,4-diMeOPh, R48=Ph, R49=Me, R50=H; 47. “q”=l, “s”=3, R47=3,4-diMeOPh, R48=Ph, R49=Me, R50=H; 48. “q”=2, “s”=l, R47=Ph, R48=Ph, R49=Me, R50=H; 49. “q”=2, “s”=l, R47=Ph, R48=Ph, R49=Me, R50=H; 50. “q”=2, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=H; 51. “q”=2, “s”=2, R47=Ph, R48=Ph, R49=Me, R50=CH3; 52. “q”=2, “s”=2, R47=Ph, R48=4-MeOPh, R49=Me, R50=H; and 53. “q”=2, “s”=2, R47=4-MeOPh, R48=4-MeOPh, R49=Me, R50=H. In some embodiments, the present disclosure provides 3-(4-methoxyphenyl)-N-(1- phenylpropan-2-yl)propan-1-amine (Compound W), or a pharmaceutically acceptable salt thereof, . In some embodiments, the present disclosure provides (S)-3-(4-methoxyphenyl)-N-(1- phenylpropan-2-yl)propan-1-amine ((S)-Compound W), or a pharmaceutically acceptable salt thereof, , with a CAS Registry Number of 2141974-01-6. In some embodiments, the present disclosure provides (S)-3-(4-methoxyphenyl)-N-(1- phenylpropan-2-yl)propan-1-amine hydrochloride. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in US20170304227, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XIX is a free base. For clarity, the definitions for the groups present in Section XIX used in the description of the compounds of Formula (XIX), and genera related thereto, have the same definitions as found in US20170304227, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XIX, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XIX) have been previously described, for example, in US20170304227, the disclosure of the publication is incorporated herein by reference in its entirety. Section XX: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XX): , or a pharmaceutically acceptable salt thereof, wherein: R51is -C(O)R52, -(C1-C6alkyl)-C(O)R52, -(C2-C4alkenyl)-C(O)R52, -NH-(C1-C4alkyl), -O-CH2-O-C(O)-(C1-C4alkyl), or , R52is -OR53or -NH-CH(-C(O)OH)-R54, R53is -H or -C1-C4alkyl, R54is -C1-C4alkyl, optionally substituted by a phenyl group, and R55is -C(O)OR53. In some embodiments, the present disclosure provides a compound having Formula (XX-A): , or a pharmaceutically acceptable salt thereof, wherein R51has the same meaning as described herein in Section XX. In some embodiments, R51is -C(O)R52, -CH2CH2-C(O)R52, -(CH2)6-C(O)R52, - CH=CH-C(O)R52, -NH-CH2CH3, -NH-CH(CH3)2, -NH-CH2CH(CH3)2, -O-CH2-O-C(O)- CH2CH3, -O-CH2-O-C(O)-CH(CH3)2, -O-CH2-O-C(O)-CH2CH(CH3)2, or R52is -OR53or -NH-CH(-C(O)OH)-R54; R53is -H or -CH(CH3)2; R54is -CH(CH3)2 or -CH2(phenyl); and R55is -C(O)OR53. Some embodiments of the present disclosure include every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, selected from the following: 4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobutanoic acid (Compound XX-1), with a CAS Registry Number of 2633638-84-1; (2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enoic acid (Compound XX-2), with a CAS Registry Number of 2633638-86-3; 8-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]-8-oxooctanoic acid (Compound XX-3), with a CAS Registry Number of 2633638-87-4; 5-([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)pyridine-3-carboxylic acid (Compound XX-4), with a CAS Registry Number of 2633638-88-5; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl butanedioate (Compound XX-5), with a CAS Registry Number of 2633638-89-6; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl (2E)-but-2-enedioate (Compound XX-6), with a CAS Registry Number of 2633638-90-9; 3-((2R,3R,11bR)-3-isobutyl-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-yl)5-isopropyl pyridine-3,5-dicarboxylate (Compound XX-7), with a CAS Registry Number of 2633638-91-0; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl (2Z)-but-2-enedioate (Compound XX-8), with a CAS Registry Number of 2633638-92-1; (2S)-2-[(2E)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]-3- methylbutanoic acid (Compound XX-9), with a CAS Registry Number of 2633638-93-2; (2S)-2-[(2E)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]-3- phenylpropanoic acid (Compound XX-10), with a CAS Registry Number of 2633638-94-3; (2S)-2-[(2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]-3- methylbutanoic acid (Compound XX-11), with a CAS Registry Number of 2633638-95-4; (2S)-2-[(2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]-3- phenylpropanoic acid (Compound XX-12), with a CAS Registry Number of 2633638-96-5; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl N-ethylcarbamate (Compound XX-13), with a CAS Registry Number of 2633639-03-7; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl N-isopropyl carbamate (Compound XX-14), with a CAS Registry Number of 2633639-04-8; (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl N-(2-methylpropyl)carbamate (Compound XX-15), with a CAS Registry Number of 2633639-05-9; [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl propanoate (Compound XX-16), with a CAS Registry Number of 2633639-06-0; [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl 2-methylpropanoate (Compound XX-17), with a CAS Registry Number of 2633639-07-1; and [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl 3-methylbutanoate (Compound XX- 18), with a CAS Registry Number of 2633639-08-2. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XX is a free base. For clarity, the definitions for the groups present in Section XX used in the description of the compounds of Formula (XX), and genera related thereto, have the same definitions as found in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XX, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XX) have been previously described, for example, in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. Section XXI: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XXI): , or a pharmaceutically acceptable salt thereof, wherein: R56is a bond, -C1-C8alkyl-, -C2-C4alkenyl-, or . In some embodiments, the present disclosure provides a compound of Formula (XXI), or a pharmaceutically acceptable salt thereof, wherein R56is a bond, -CH2CH2-, - (CH2)6-, -CH=CH-, or . In some embodiments, the present disclosure provides 3,5-bis-[(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- yl]pyridine-3,5-dicarboxylate, or a pharmaceutically acceptable salt thereof (Compound XXI-1), with a CAS Registry Number of 2633638-97-6. In some embodiments, the present disclosure provides bis-[(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] octanedioate (Compound XXI-2), or a pharmaceutically acceptable salt thereof, with a CAS Registry Number of 2633638-98-7. In some embodiments, the present disclosure provides [(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] butanedioate (Compound XXI-3), or a pharmaceutically acceptable salt thereof, with a CAS Registry Number of 2633638-99-8. In some embodiments, the present disclosure provides bis-[(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] (2E)-but-2-enedioate (Compound XXI-4), or a pharmaceutically acceptable salt thereof, with a CAS Registry Number of 2633639-00-4. In some embodiments, the present disclosure provides bis-[(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] (2Z)-but-2-enedioate (Compound XXI-5), or a pharmaceutically acceptable salt thereof, with a CAS Registry Number of 2633639-01-5. In some embodiments, the present disclosure provides bis[(2R,3R,11bR)-9,10- dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] oxalate (Compound XXI-6), or a pharmaceutically acceptable salt thereof, with a CAS Registry Number of 2633639-02-6. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XXI is a free base. For clarity, the definitions for the groups present in Section XXI used in the description of the compounds of Formula (XXI), and genera related thereto, have the same definitions as found in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XXI, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XXI) have been previously described, for example, in US20210087191, the disclosure of the publication is incorporated herein by reference in its entirety. Section XXII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2018222549, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XXII): , or a pharmaceutically acceptable salt thereof, wherein: R57is C1-C4alkyl and is optionally substituted with one or more deuterium atoms; W is18F or19F; and Y is -(CRaRb)r-, wherein Raand Rbare each independently hydrogen or deuterium atoms, “r” is an integer from 1 to 6; provided that at least one deuterium atom is present at either R57or Y; and provided that when “r” is 2, R57is not CH3. In some embodiments, the present disclosure provides a compound of Formula (XXII), wherein “r” is 3, 4, 5, or 6. In some embodiments, “r” is 3. In some embodiments, Y is -(CH2)2-, -(CD2)2-, - (CH2)3-, -(CD2)3-, -(CH2)4-, -(CD2)4-, -(CH2)5-, -(CD2)5-, -(CH2)6-, or -(CD2)6-. In some embodiments, Y is -(CH2)3- or -(CD2)3-. In some embodiments, the present disclosure provides a compound of Formula (XXII) wherein R57is C1-C4alkyl that can be deuterated or non-deuterated. In some embodiments, R57is -CH3, -CD3, -CH2CH3, -CD2CD3, -CD2CH3, -CH2CD3, - CH(CH3)2, -CD(CD3)2, -CH(CD3)2, -CD(CH3)2, -CH2CH(CH3)2, -CD2CH(CH3)2, -CH2CD(CH3)2, - CH2CH(CD3)2, -CD2CD(CH3)2, -CD2CH(CD3)2, -CH2CD(CD3)2, or -CD2CD(CD3)2. In some of these embodiments, R57is -CD3, -CD2CD3, -CD2CH3, -CH2CD3, - CD(CD3)2, -CH(CD3)2, -CD(CH3)2, -CD2CH(CH3)2, -CH2CD(CH3)2, -CH2CH(CD3)2, - CD2CD(CH3)2, -CD2CH(CD3)2, -CH2CD(CD3)2, or -CD2CD(CD3)2. In some embodiments, R57is -CH3 or -CD3. In some embodiments, R57is -CD3. In some embodiments, the present disclosure provides a compound having Formula (XXII-A): , or a pharmaceutically acceptable salt thereof, wherein W is18F or19F. In some embodiments, the present disclosure provides a compound having Formula (XXII-B): , or a pharmaceutically acceptable salt thereof, wherein W is18F or19F. In some embodiments, W is F. In some embodiments, W is18F. In some embodiments, W is19F. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2018222549, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XXII is a free base. For clarity, the definitions for the groups present in Section XXII used in the description of the compounds of Formula (XXII), and genera related thereto, have the same definitions as found in WO2018222549, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XXII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XXII) have been previously described, for example, in WO2018222549, the disclosure of the publication is incorporated herein by reference in its entirety. Section XXIII: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2016019312, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the present disclosure provides a compound having Formula (XXIII): , or a pharmaceutically acceptable salt thereof, wherein: X1is a substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl; Z is N or CH; “w” is 1, 2, or 3; “Ar” is substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl; R58is H, ethyl ester, isopropyl ester, -C(O)-alkyl (i.e., methyl ketone, ethyl ketone, etc.), or substituted or unsubstituted 5-membered heteroaryl; and R59is H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; wherein the bond between the carbon atoms bearing “Ar” and R58is a single or double bond. In some embodiments, the bond between the carbon atoms bearing the “Ar” Group and the R58Group is a single bond, and the groups labeled “Ar” and R58are in an R,R- configuration, an S,S-configuration, an S,R-configuration, or an R,S-configuration. In some embodiments, the bond between the carbon atoms bearing Ar and R58is a double bond. In some embodiments, the present disclosure provides a compound having Formula (XXIII-A): , or a pharmaceutically acceptable salt thereof, wherein X2, X3, X4, and X5are independently H, alkyl, substituted alkyl, aryl, substituted aryl, halo, alkoxy, haloalkyl, haloalkoxy, ester, keto, hydroxyl, amino, substituted amino, amido, or nitro. In some embodiments, the present disclosure provides a compound having Formula (XXIII-B): , or a pharmaceutically acceptable salt thereof, wherein X2, X3, X4, and X5are independently H, alkyl, substituted alkyl, aryl, substituted aryl, halo, alkoxy, haloalkyl, haloalkoxy, ester, keto, hydroxyl, amino, substituted amino, amido, or nitro. In some embodiments, X2, X3, X4, and X5are independently H, methyl, ethyl, isopropyl, [1,4]dioxin-5-yl, fluoro, chloro, trifluoromethyl, amino, dimethylamino, methylamido, nitro, azo, benzyl, 2-phenyl, ethyl, pyrrolyl, ethyl ester, 1-hydroxyethyl, hydroxyl, methoxy, trifluoromethoxy, or tert-butoxycarbonylamino. In some embodiments, X2and X3are H, and X4and X5are independently H, fluoro, or trifluoromethyl. In some embodiments, the present disclosure provides a compound having Formula (XXIII-C): , or a pharmaceutically acceptable salt thereof, wherein X4is halo, and “w” is 2 or 3. In some embodiments, X4is fluoro. In some embodiments, the present disclosure provides a compound having Formula (XXIII-D): , or a pharmaceutically acceptable salt thereof, wherein X4is halo, and “w” is 2 or 3. In some embodiments, X4is fluoro. In some embodiments, the present disclosure provides a compound having Formula (XXIII-E): , or a pharmaceutically acceptable salt thereof, wherein R59ais H, methyl, ethyl, or 2- benzylethyl, wherein R59bis H or halo, and wherein X4and X5are independently H or halo. In some embodiments, the present disclosure provides a compound having Formula (XXIII-F): , or a pharmaceutically acceptable salt thereof, wherein R59ais H, methyl, ethyl, or 2- benzylethyl, wherein R59bis H or halo, and wherein X4and X5are independently H or halo. In some embodiments, the present disclosure provides a compound having Formula (XXIII-G): , or a pharmaceutically acceptable salt thereof, wherein X2, X3, X4, and X5are independently H, halo, or haloalkyl, and wherein R59is H or alkyl. In some embodiments, the present disclosure provides a compound having Formula (XXIII-H): , or a pharmaceutically acceptable salt thereof, wherein X2, X3, X4, and X5are independently H, halo, or haloalkyl, and wherein R59is H or alkyl. In some embodiments, R59is H, X2and X3are H, and X4and X5are independently H, fluoro, or trifluoromethyl. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2016019312, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the compound in Section XXIII is a free base. For clarity, the definitions for the groups present in Section XXIII used in the description of the compounds of Formula (XXIII), and genera related thereto, have the same definitions as found in WO2016019312, the disclosure of the publication is incorporated herein by reference in its entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XXIII, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XXIII) have been previously described, for example, in WO2016019312, the disclosure of the publication is incorporated herein by reference in its entirety. Section XXIV: VMAT2 Inhibitors In some embodiments, the present disclosure provides VMAT2 inhibitors, or a pharmaceutically acceptable salt thereof, as described in WO2021027792 or EP4015517, the disclosures of the publications are incorporated herein by reference in their entirety. In some embodiments, the present disclosure provides a compound having Formula (XXIV): , or a pharmaceutically acceptable salt thereof, wherein: “---” represents: a single bond or a double bond; when “---” is a single bond, R60is selected from OH, H, or when “---” is a double bond, R60is O; R61is selected from hydrogen, methyl, or ethyl; R62is selected from C2-C10alkyl, C3-C6cycloalkyl, C3-C6cycloalkyl-C1-C6alkyl, 3- to 6-membered heterocycloalkyl-C1-C3alkyl, C2-C6alkenyl or C1-C6heteroalkyl unsubstituted, or substituted with 1, 2, or 3 R63groups; and R63is selected from F, Cl, Br, OH, SH, or NH2. In some embodiments, “---” is a single bond and R60is OH or . In some embodiments, “---” is a single bond and R60is OH. In some embodiments, “---” is a double bond and R60is O. In some embodiments, the stereochemistry for the compound of Formula (XXIV) is 2R,3R,11bR, wherein “---”, R61, R62, and R63have the same meaning as described herein in Section XXIV. In some embodiments, the stereochemistry for the compound of Formula (XXIV) is 2S,3R,11bR wherein “---”, R61, R62, and R63have the same meaning as described herein in Section XXIV. Some embodiments include every combination of one or more compounds selected from the following group of compounds shown in TABLE XXIV-A. TABLE XXIV-A

[0011] In some embodiments, the present disclosure provides (2R,3R,11bR)-3-isobutyl-10- methoxy-9-(2,2,2-trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-1), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2S,3S,11bS)-3-isobutyl-10- methoxy-9-(2,2,2-trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-2), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-3-isobutyl-10- methoxy-9-(2,2,2-trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-yl L-valinate (Compound XXIV-3), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9- (cyclopropylmethoxy)-3-isobutyl-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound XXIV-4), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2S,3S,11bS)-9- (cyclopropylmethoxy)-3-isobutyl-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound XXIV-5), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides (2R,3R,11bR)-9- (cyclopropylmethoxy)-3-isobutyl-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-yl L-valinate (Compound XXIV-6), or a pharmaceutically acceptable salt thereof. In some embodiments, the present disclosure provides every combination of one or more compounds, or a pharmaceutically acceptable salt thereof, disclosed in WO2021027792 or EP4015517, the disclosures of the publications are incorporated herein by reference in their entirety. In some embodiments, the compound in Section XXIV is a free base. For clarity, the definitions for the groups present in Section XXIV used in the description of the compounds of Formula (XXIV), and genera related thereto, have the same definitions as found in WO2021027792 or EP4015517, the disclosures of the publications are incorporated herein by reference in their entirety. In some embodiments, the vesicular monoamine transporter 2 (VMAT2) inhibitor in Section XXIV, or a pharmaceutically acceptable salt thereof, is administered orally. Methods for preparing compounds of Formula (XXIV) have been previously described, for example, in WO2021027792 or EP4015517, the disclosures of the publications are incorporated herein by reference in their entirety. Formulations for Compound A and Pharmaceutically Acceptable Salts thereof Formulation 1 (Compound A and Pharmaceutically Acceptable Salts thereof) In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 5% w / w and about 15% w / w of the solid oral pharmaceutical formulation. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 8% w / w and about 12% w / w of the solid oral pharmaceutical formulation. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of about 9.5% w / w of the solid oral pharmaceutical formulation. In some embodiments of Formulation 1, the solid oral pharmaceutical formulation comprises: between about 75% w / w and about 85% w / w of the at least one diluent; between about 1% w / w and about 5% w / w of the at least one binder; between about 3% w / w and about 8% w / w of the at least one disintegrant; and between about 0.5% w / w and about 3% w / w of the at least one lubricant. In some embodiments of Formulation 1, the at least one diluent is chosen from microcrystalline cellulose, dibasic calcium phosphate, silicified microcrystalline cellulose, isomalt, lactose, mannitol, and pregelatinized maize starch. In some embodiments, the at least one diluent is microcrystalline cellulose. In some embodiments, the at least one diluent is dibasic calcium phosphate. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate. In some embodiments of Formulation 1, the solid oral pharmaceutical formulation comprises between about 80% w / w and about 85% w / w of the at least one diluent. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate, and the solid oral pharmaceutical formulation comprises about 81% w / w of the at least one diluent. In some embodiments of Formulation 1, the at least one disintegrant is chosen from croscarmellose sodium, sodium starch glycolate (Type A or B), crospovidone, microcrystalline cellulose, carboxymethylcellulose, and hydroxypropyl cellulose. In some embodiments, the at least one disintegrant is croscarmellose sodium. In some embodiments, the solid oral pharmaceutical formulation comprises between about 4% w / w and about 7% w / w of the at least one disintegrant. In some embodiments, the at least one disintegrant is croscarmellose sodium and the solid oral pharmaceutical formulation comprises about 5% w / w of the at least one disintegrant. In some embodiments of Formulation 1, the at least one binder is chosen from hydroxypropylmethyl cellulose (hypromellose), polyvinylpyrrolidone, starch, sucrose, mannitol, polyethylene glycol, cellulose and cellulose derivatives. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose). In some embodiments, the solid oral pharmaceutical formulation comprises between about 2% w / w and about 4% w / w of the at least one binder. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose) and the solid oral pharmaceutical formulation comprises about 3% w / w of the at least one binder. In some embodiments of Formulation 1, the at least one lubricant is chosen from magnesium stearate, stearic acid, talc, glyceryl behenate, and sodium lauryl sulfate. In some embodiments, the at least one lubricant is magnesium stearate. In some embodiments, the solid oral pharmaceutical formulation comprises between about 0.5% w / w and about 2% w / w of the at least one lubricant. In some embodiments, the at least one lubricant is magnesium stearate and the solid oral pharmaceutical formulation comprises about 1% w / w of the at least one lubricant. In some embodiments of Formulation 1, the solid oral pharmaceutical formulation comprises: Compound A, or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 9.5% w / w of the solid oral pharmaceutical formulation; the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate and is present in an amount of about 81% w / w of the solid oral pharmaceutical formulation; the at least one disintegrant is croscarmellose sodium and is present in an amount of about 5% w / w of the solid oral pharmaceutical formulation; the at least one binder is hydroxypropylmethyl cellulose (hypromellose) and is present in an amount of about 3% w / w of the solid oral pharmaceutical formulation; and the at least one lubricant is magnesium stearate and is present in an amount of about 1% w / w of the solid oral pharmaceutical formulation. In some embodiments, the dibasic calcium phosphate is anhydrous. Also provided is a solid oral pharmaceutical formulation, comprising: a compound having the structure or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 9.5% w / w of the formulation; microcrystalline cellulose in an amount of about 67.5% w / w of the formulation; anhydrous dibasic calcium phosphate in an amount of about 14% w / w of the formulation; hydroxypropylmethyl cellulose (hypromellose) in an amount of about 3% w / w of the formulation; croscarmellose sodium in an amount of about 5% w / w of the formulation; and magnesium stearate in an amount of about 1% w / w of the formulation. In some embodiments, the amount of cis-Compound A or a pharmaceutically acceptable salt thereof, is about 10 mg based on the cis-Compound A free base. In some embodiments, the solid oral pharmaceutical formulation provides an AUC0-inf of cis- Compound A from about 97 h x ng / mL to about 179 h x ng / mL when the pharmaceutical formulation is administered to a subject. In some further embodiments, the AUC0-inf is from about 110 h x ng / mL to about 166 h x ng / mL. In some further embodiments, the AUC0-inf is about 138 h x ng / mL. In some embodiments, the amount of cis-Compound A or a pharmaceutically acceptable salt thereof, is about 10 mg based on the cis-Compound A free base. In some embodiments, the solid oral pharmaceutical formulation provides a Cmaxof cis-Compound A from about 10 ng / mL to about 19 ng / mL when the pharmaceutical formulation is administered to a subject. In some further embodiments, the Cmax is from about 12 ng / mL to about 17 ng / mL. In some further embodiments, the Cmax is about 15 ng / mL. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis-Compound A. In some embodiments, the citrate salt of cis-Compound A is crystalline. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:1. In some embodiments, the cis-Compound A citrate monohydrate is crystalline. Formulation 2 (Compound A and Pharmaceutically Acceptable Salts thereof) In some embodiments of Formulation 2, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 15% w / w and about 25% w / w of the solid oral pharmaceutical formulation. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 18% w / w and about 20% w / w of the solid oral pharmaceutical formulation. In some embodiments, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of about 19% w / w of the solid oral pharmaceutical formulation. In some embodiments of Formulation 2, the solid oral pharmaceutical formulation comprises: between about 65% w / w and about 75% w / w of the at least one diluent; between about 1% w / w and about 5% w / w of the at least one binder; between about 3% w / w and about 8% w / w of the at least one disintegrant; and between about 0.5% w / w and about 3% w / w of the at least one lubricant. In some embodiments of Formulation 2, the at least one diluent is chosen from microcrystalline cellulose, dibasic calcium phosphate, silicified microcrystalline cellulose, isomalt, lactose, mannitol, and pregelatinized maize starch. In some embodiments, the at least one diluent is microcrystalline cellulose. In some embodiments, the at least one diluent is dibasic calcium phosphate. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate. In some embodiments, the solid oral pharmaceutical formulation comprises between about 70% w / w and about 73% w / w of the at least one diluent. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate, and the solid oral pharmaceutical formulation comprises about 72% w / w of the at least one diluent. In some embodiments of Formulation 2, the at least one disintegrant is chosen from croscarmellose sodium, sodium starch glycolate (Type A or B), crospovidone, microcrystalline cellulose, carboxymethylcellulose, and hydroxypropyl cellulose. In some embodiments, the at least one disintegrant is croscarmellose sodium. In some embodiments, the solid oral pharmaceutical formulation comprises between about 4% w / w and about 7% w / w of the at least one disintegrant. In some embodiments, the at least one disintegrant is croscarmellose sodium and the solid oral pharmaceutical formulation comprises about 5% w / w of the at least one disintegrant. In some embodiments of Formulation 2, the at least one binder is chosen from hydroxypropylmethyl cellulose (hypromellose), polyvinylpyrrolidone, starch, sucrose, mannitol, polyethylene glycol, cellulose and cellulose derivatives. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose). In some embodiments, the solid oral pharmaceutical formulation comprises between about 2% w / w and about 4% w / w of the at least one binder. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose) and the solid oral pharmaceutical formulation comprises about 3% w / w of the at least one binder. In some embodiments of Formulation 2, the at least one lubricant is chosen from magnesium stearate, stearic acid, talc, glyceryl behenate, and sodium lauryl sulfate. In some embodiments, the at least one lubricant is magnesium stearate. In some embodiments, the solid oral pharmaceutical formulation comprises between about 0.5% w / w and about 2% w / w of the at least one lubricant. In some embodiments, the at least one lubricant is magnesium stearate, and the solid oral pharmaceutical formulation comprises about 1% w / w of the at least one lubricant. In some embodiments of Formulation 2, the solid oral pharmaceutical formulation comprises: Compound A, or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 19% by weight of the solid oral pharmaceutical formulation; the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate and is present in an amount of about 72% w / w of the solid oral pharmaceutical formulation; the at least one disintegrant is croscarmellose sodium and is present in an amount of about 5% w / w of the solid oral pharmaceutical formulation; the at least one binder is hydroxypropyl methyl cellulose (hypromellose) and is present in an amount of about 3% w / w of the solid oral pharmaceutical formulation; and the at least one lubricant is magnesium stearate and is present in an amount of about 1% w / w of the solid oral pharmaceutical formulation. In some embodiments, the dibasic calcium phosphate is anhydrous. Also provided is a solid oral pharmaceutical formulation, comprising: a compound having the structure: or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 18.9% w / w of the formulation; microcrystalline cellulose in an amount of about 64.1% w / w of the formulation; anhydrous dibasic calcium phosphate in an amount of about 8% w / w of the formulation; hydroxypropylmethyl cellulose (hypromellose) in an amount of about 3% w / w of the formulation; croscarmellose sodium in an amount of about 5% w / w of the formulation; and magnesium stearate in an amount of about 1% w / w of the formulation. In some embodiments, the amount of cis-Compound A or a pharmaceutically acceptable salt thereof, is about 20 mg based on the cis-Compound A free base. In some embodiments, the solid oral pharmaceutical formulation provides an AUC0-inf of cis- Compound A from about 193 h x ng / mL to about 357 h x ng / mL when the pharmaceutical formulation is administered to a subject. In some further embodiments, the AUC0-inf is from about 220 h x ng / mL to about 330 h x ng / mL. In some further embodiments, the AUC0-inf is about 292 h x ng / mL. In some embodiments, the amount of cis-Compound A or a pharmaceutically acceptable salt thereof, is about 20 mg based on the cis-Compound A free base. In some embodiments, the solid oral pharmaceutical formulation provides a Cmaxof cis-Compound A from about 36 ng / mL to about 68 ng / mL when the pharmaceutical formulation is administered to a subject. In some further embodiments, the Cmax is from about 46 ng / mL to about 58 ng / mL. In some further embodiments, the Cmax is about 53 ng / mL. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis-Compound A. In some embodiments, the citrate salt of cis-Compound A is crystalline. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:1. In some embodiments, the cis-Compound A citrate monohydrate is crystalline. Formulation 3 (Compound A and Pharmaceutically Acceptable Salts thereof) In some embodiments of Formulation 3, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 25% w / w and about 35% w / w of the solid oral pharmaceutical formulation. In some embodiments of Formulation 3, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of between about 27% w / w and about 30% w / w of the solid oral pharmaceutical formulation. In some embodiments of Formulation 3, Compound A, or a pharmaceutically acceptable salt thereof, is present in the formulation at a level (based on the free base) of about 28% w / w of the solid oral pharmaceutical formulation. In some embodiments of Formulation 3, the solid oral pharmaceutical formulation comprises: between about 55% w / w and about 70% w / w of the at least one diluent; between about 1% w / w and about 5% w / w of the at least one binder; between about 3% w / w and about 8% w / w of the at least one disintegrant; and between about 0.5% w / w and about 3% w / w of the at least one lubricant. In some embodiments of Formulation 3, the at least one diluent is chosen from microcrystalline cellulose, dibasic calcium phosphate, silicified microcrystalline cellulose, isomalt, lactose, mannitol, and pregelatinized maize starch. In some embodiments, the at least one diluent is microcrystalline cellulose. In some embodiments, the at least one diluent is dibasic calcium phosphate. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate. In some embodiments, the solid oral pharmaceutical formulation comprises between about 60% w / w and about 65% w / w of the at least one diluent. In some embodiments, the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate, and the solid oral pharmaceutical formulation comprises about 63% w / w of the at least one diluent. In some embodiments of Formulation 3, the at least one disintegrant is chosen from croscarmellose sodium, sodium starch glycolate (Type A or B), crospovidone, microcrystalline cellulose, carboxymethylcellulose, and hydroxypropyl cellulose. In some embodiments, the at least one disintegrant is croscarmellose sodium. In some embodiments, the solid oral pharmaceutical formulation comprises between about 4% w / w and about 7% w / w of the at least one disintegrant. In some embodiments, the at least one disintegrant is croscarmellose sodium and the solid oral pharmaceutical formulation comprises about 5% w / w of the at least one disintegrant. In some embodiments of Formulation 3, the at least one binder is chosen from hydroxypropylmethyl cellulose (hypromellose), polyvinylpyrrolidone, starch, sucrose, mannitol, polyethylene glycol, cellulose and cellulose derivatives. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose). In some embodiments, the solid oral pharmaceutical formulation comprises between about 2% w / w and about 4% w / w of the at least one binder. In some embodiments, the at least one binder is hydroxypropylmethyl cellulose (hypromellose) and the solid oral pharmaceutical formulation comprises about 3% w / w of the at least one binder. In some embodiments of Formulation 3, the at least one lubricant is chosen from magnesium stearate, stearic acid, talc, glyceryl behenate, and sodium lauryl sulfate. In some embodiments, the at least one lubricant is magnesium stearate. In some embodiments, the solid oral pharmaceutical formulation comprises between about 0.5% w / w and about 2% w / w of the at least one lubricant. In some embodiments, the at least one lubricant is magnesium stearate, and the solid oral pharmaceutical formulation comprises about 1% w / w of the at least one lubricant. In some embodiments of Formulation 3, the solid oral pharmaceutical formulation comprises: Compound A, or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 28% by weight of the solid oral pharmaceutical formulation; the at least one diluent is microcrystalline cellulose and dibasic calcium phosphate, and is present in an amount of about 63% w / w of the solid oral pharmaceutical formulation; the at least one disintegrant is croscarmellose sodium and is present in an amount of about 5% w / w of the solid oral pharmaceutical formulation; the at least one binder is hydroxypropylmethyl cellulose (hypromellose) and is present in an amount of about 3% w / w of the solid oral pharmaceutical formulation; and the at least one lubricant is magnesium stearate and is present in an amount of about 1% w / w of the solid oral pharmaceutical formulation. In some embodiments, the dibasic calcium phosphate is anhydrous. Also provided is a solid oral pharmaceutical formulation comprising: a compound having the structure: or a pharmaceutically acceptable salt thereof, at a level (based on the free base) of about 28.4% w / w of the formulation; microcrystalline cellulose in an amount of about 54.6% w / w of the formulation; anhydrous dibasic calcium phosphate in an amount of about 8% w / w of the formulation; hydroxypropylmethyl cellulose (hypromellose) in an amount of about 3% w / w of the formulation; croscarmellose sodium in an amount of about 5% w / w of the formulation; and magnesium stearate in an amount of about 1% w / w of the formulation. In some embodiments, the amount of cis-Compound A or a pharmaceutically acceptable salt thereof, is about 30 mg based on the cis-Compound A free base. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis-Compound A. In some embodiments, the citrate salt of cis-Compound A is crystalline. In some embodiments, Compound A or cis-Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:1. In some embodiments, the cis-Compound A citrate monohydrate is crystalline. In some embodiments, the present disclosure provides a compound of any Formulae disclosed herein, or a pharmaceutically acceptable salt thereof, wherein the compound is an enantiomer, optical isomer, diastereomer, N-oxide, crystalline form, solvate, or hydrate thereof. `While it may be possible for the compounds and salts of the subject disclosure to be administered as the raw chemical, it is also possible to present them as a pharmaceutical formulation. Accordingly, provided herein are pharmaceutical formulations which comprise one or more of certain compounds disclosed herein, or one or more pharmaceutically acceptable salts thereof, together with one or more pharmaceutically acceptable carriers thereof and optionally one or more other therapeutic ingredients. The carrier(s) must be “acceptable” in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof. Proper formulation is dependent upon the route of administration chosen. Any of the well-known techniques, carriers, and excipients may be used as suitable and as understood in the art. The pharmaceutical formulations disclosed herein may be manufactured in any manner known in the art, e.g., by means of conventional mixing, dissolving, granulating, dragee-making, levigating, emulsifying, encapsulating, entrapping, or compression processes. Examples of embodiments of the present disclosure are provided in the following examples. The following examples are presented only by way of illustration and to assist one of ordinary skill in using the disclosure. The examples are not intended in any way to otherwise limit the scope of the disclosure. EXAMPLES EXAMPLE 1 This was a Phase 2, multicenter, randomized, double-blind, placebo-controlled, inpatient study designed to assess the efficacy, safety, tolerability, and pharmacokinetics (PK) of cis-Compound A compared with placebo in adult subjects with a primary diagnosis of schizophrenia, who were experiencing an acute exacerbation or relapse of symptoms (Positive and Negative Syndrome Scale [PANSS] total score ≥80). The study included a Screening Period (washout duration of at least 5 half-lives of any antipsychotic and / or prohibited medications), a 6-week randomized Double-Blind Treatment Period, and a 2-week post-treatment Safety Follow-Up Period. Approximately 213 subjects, 18 to 55 years of age (inclusive), were enrolled for study participation. Subjects were initially randomized 1:1:1 to receive placebo, cis-Compound A 20 mg, or 40 mg capsules once a day (QD) in a 6-week Double-Blind Treatment Period. Doses of 60 mg QD or 20 mg twice a day (BID), and 30 mg BID were also evaluated based on the results of 2 planned interim analyses. If any dose group was added or dropped based on the results of the interim analyses, then the randomization ratio and total number of subjects per group were adjusted to maintain an approximate 1:2 randomization ratio for placebo to active treatment throughout the study. Any antipsychotic and / or prohibited medications were washed out prior to randomization. Subjects who routinely take long-acting injectable (LAI) antipsychotic medications did not receive a dose of medication for at least 1.5 injection cycles prior to screening. Eligible subjects were housed in an inpatient study center for up to 10 weeks to monitor the efficacy, safety, tolerability, and PK of cis- Compound A. Adverse events (AEs) were assessed throughout the study, and changes in vital signs (blood pressure and heart rate) and electrocardiograms (ECGs) were monitored. Dose tolerability was assessed throughout the 6-week Double-Blind Treatment Period and a 2- week post-treatment Safety Follow-Up Period was conducted after the final dose of study treatment. The end of study was the last scheduled visit assessment or procedure of the last subject in the study globally. Screening Period Subjects were admitted into the inpatient facility at the time of screening. The Screening Period was a washout duration of at least 5 half-lives of any antipsychotic and / or prohibited medications, and subjects were randomized as soon as confirmed to meet all eligibility criteria. Subjects and informants provided written informed consent. Subjects met the criteria for a primary diagnosis of schizophrenia, as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition Text Revision (DSM-5-TR) (American Psychiatric Association, 2022) and confirmed by the Mini International Neuropsychiatric Interview (MINI) for Schizophrenia and Psychotic Disorder Studies, Version 7.0.2. Subjects were required to washout any antipsychotic and / or prohibited medications for a duration of at least 5 half-lives of those medications in use prior to Day-1. Subjects who routinely took LAI antipsychotic medications must not have received a dose of medication for at least 1.5 injection cycles prior to screening. During screening and prior to randomization, subjects who took antipsychotics and / or other prohibited medications discontinued these medication(s) in a manner that was consistent with labeling recommendations and conventional medical practices. Double-Blind Treatment Period Subjects were initially randomized in a 1:1:1 ratio to receive placebo, cis-Compound A 20 mg QD, or 40 mg QD for 6 weeks. Subjects were randomized via an interactive web response system (IWRS). In addition, dose group(s) of 60 mg QD or 20 mg BID, and 30 mg BID were added based on the results of interim analyses. This was a fixed-dose titration study. Each subject in the 40 or 60 mg QD dose groups showed signs that cis-Compound A was tolerated before titrating to a higher dose on Day 8. Those subjects meeting titration hold criteria remained on their current dose until tolerability was established (i.e., no longer meeting titration hold criteria). If tolerability to the assigned higher dose was not achieved by Day 14, the subject continued on the current dose for the remainder of the study. Subjects were dosed as follows: • 20 mg QD dose group: Subjects received 20 mg QD for 6 weeks. • 40 mg QD dose group: o Days 1 to 7: Subjects received 20 mg QD. o Days 8 to 42: Subjects received 40 mg QD. Subjects had to have demonstrated tolerability before titrating to this higher dose. • 60 mg QD dose group: o Days 1 to 7: Subjects received 40 mg QD. o Days 8 to 42: Subjects received 60 mg QD. Subjects had to have demonstrated tolerability before titrating to this higher dose. • 20 mg BID dose group: Subjects received 20 mg BID for 6 weeks. • 30 mg BID dose group: Subjects received 30 mg BID for 6 weeks. Titration Hold Criteria Subjects were held at the current dose (titration dose) if any titration hold criteria were met at any point on the previous dosing day or on the current dosing day prior to the evening dose: • Subject’s dose was reduced. • Supine or standing heart rate >110 bpm continuously for >2 hours and ≤5 hours. • Supine o...

Claims

What is claimed is:

1. A method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

2. A method of treating behavioral problems associated with a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

3. A method of improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder in a subject in need thereof, comprising administering to the subject a dosing regimen of a compound having the structure:,or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

4. A compound having the structure of:, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use: (i) in a method of treating a neurological or psychiatric disease or disorder; (ii) in a method of treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) in improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

5. Use of a compound having the structure of:, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for: (i) treating a neurological or psychiatric disease or disorder; (ii) treating behavioral problems associated with a neurological or psychiatric disease or disorder; or (iii) improving behavioral and / or psychological symptoms of a neurological or psychiatric disease or disorder; in a subject in need thereof, wherein Compound A, or a pharmaceutically acceptable saltthereof, is administered by following a dosing regimen, and wherein the dosing regimen comprises a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

6. A compound for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base; wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

7. A compound for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

8. A compound for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, the compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base, wherein: the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, in combination with a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof.

9. A vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

10. A vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

11. A vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof, wherein the method comprises administering to the subject a dosing regimen of a compound having the structure:, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

12. A multi-pack for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

13. A multi-pack for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein themethod comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

14. A multi-pack for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

15. A pharmaceutical composition for use in a method of treating a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

16. A pharmaceutical composition for use in a method of treating a behavioral problem associated with a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

17. A pharmaceutical composition for use in a method of improving a behavioral and / or psychological symptom of a neurological or psychiatric disease or disorder in a subject in need thereof comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the method comprises administering to the subject a dosing regimen of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

18. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein the neurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar disorder, Parkinson’s disease (or synucleinopathies) psychosis, obsessive-compulsive disorder, obsessive-compulsive disorder, treatment-refractory obsessive-compulsive, disorder, and autism spectrum disorder.

19. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein theneurological or psychiatric disease or disorder is chosen from schizophrenia or schizoaffective disorder, adjunctive treatment of schizophrenia, Alzheimer’s disease psychosis, bipolar I disorder, Parkinson’s disease (or synucleinopathies) psychosis, and obsessive-compulsive disorder.

20. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 18 or 19, wherein the neurological or psychiatric disease or disorder is schizophrenia or schizoaffective disorder.

21. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 20, wherein the subject has at least one sign or symptom of schizophrenia.

22. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 21, wherein the subject has at least one positive, negative, and / or cognitive sign, or symptom of schizophrenia.

23. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 21 or 22, wherein the at least one sign or symptom is delusions, hallucinations, disorganized speech, disorganized behavior or attention, anhedonia, catatonic behavior, affective flattening, alogia, avolition, conceptual disorganization, or any combination thereof.

24. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 20, wherein the subject is also being administered at least one co-therapeutic agent for the treatment of schizophrenia and the neurological or psychiatric disease or disorder is adjunctive treatment of schizophrenia (ATS).

25. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 24, wherein the subject has a stable background antipsychotic medication dose.

26. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 24, wherein the subject is residually symptomatic or has at least one residual sign or symptom after first- or second-line treatment of schizophrenia.

27. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 24, wherein the subject is residually symptomatic or has at least one residual sign or symptom after mono- or combination therapy for schizophrenia.

28. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 24, wherein the mono- or combination therapy is initial therapy.

29. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 24, wherein the at least one co-therapeutic agent is least one antipsychotic agent.

30. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 29, wherein the antipsychotic agent is a typical antipsychotic agent.

31. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 30, wherein the typical antipsychotic agent is benperidol, chlorpromazine, droperidol, flupentixol, fluphenazine, haloperidol, levomepromazine, loxapine, molindone, pericyazine, perphenazine, pimozide, prochlorperazine, promazine, sulpiride, thiothixene, trifluoperazine, thioridazine, zuclopenthixol, or any combination thereof.

32. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 29, wherein the antipsychotic agent is an atypical antipsychotic agent.

33. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 32, wherein the atypical antipsychotic agent is clozapine, olanzapine, risperidone, sertindole, quetiapine, paliperidone, asenapine, ziprasidone, surmontil, iloperidone, aripiprazole, or any combination thereof.

34. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base.

35. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 34, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base.

36. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 35, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base.

37. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 36, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base.

38. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 34, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

39. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 38, wherein the dosing regimen comprisesadministration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base.

40. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 38, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base.

41. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 38, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base.

42. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 38, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base.

43. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 38, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base.

44. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein the dosing regimen does not include any titration period.

45. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises once a day (QD) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base.

46. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 45, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base.

47. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 46, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base.

48. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 47, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base.

49. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 48, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

50. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 49, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base.

51. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 49, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base.

52. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 49, wherein the dosing regimen comprises QDadministration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base.

53. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 49, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base.

54. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 49, wherein the dosing regimen comprises QD administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base.

55. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 45 to 54, wherein the dosing regimen does not include any titration period.

56. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises two times a day (BID) administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base.

57. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 56, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base.

58. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 57, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base.

59. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 58, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base.

60. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 56, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

61. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 60, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 10 mg of Compound A free base.

62. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 60, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 15 mg of Compound A free base.

63. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 60, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 20 mg of Compound A free base.

64. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 60, wherein the dosing regimen comprises BID administration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 25 mg of Compound A free base.

65. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 60, wherein the dosing regimen comprises BIDadministration of Compound A, or a pharmaceutically acceptable salt thereof, at a daily dose equivalent to about 30 mg of Compound A free base.

66. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 56 to 65, wherein the dosing regimen does not include any titration period.

67. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period.

68. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 67, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, during the titration period, at an initial daily dose equivalent to from about 10% to about 70% of the final daily dose in the final dose period, and then administration of Compound A, or a pharmaceutically acceptable salt thereof, at the final daily dose.

69. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 68, wherein the initial daily dose in the titration period is equivalent to from about 20% to about 60% of the final daily dose.

70. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 69, wherein the initial daily dose in the titration period is equivalent to about 25% or about 50% of the final daily dose.

71. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 70, wherein the initial daily dose in the titration period is equivalent to about 25% of the final daily dose.

72. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 70, wherein the initial daily dose in the titration period is equivalent to about 50% of the final daily dose.

73. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 68, wherein the initial daily dose in the titration period is about 2.5 mg, about 5 mg, about 7.5 mg, about 10 mg, about 12.5 mg, about 15 mg, about 17.5 mg, or about 20 mg of Compound A free base.

74. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 73, wherein the initial daily dose in the titration period is about 2.5 mg, about 5 mg, about 7.5 mg, or about 10 mg of Compound A free base.

75. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 74, wherein the initial daily dose in the titration period is about 2.5 mg of Compound A free base.

76. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 74, wherein the initial daily dose in the titration period is about 5 mg of Compound A free base.

77. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 74, wherein the initial daily dose in the titration period is about 7.5 mg of Compound A free base.

78. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 74, wherein the initial daily dose in the titration period is about 10 mg of Compound A free base.

79. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 78, wherein the final daily dose is from about 5 mg to about 70 mg of Compound A free base.

80. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 79, wherein the final daily dose is from about 5 mg to about 40 mg of Compound A free base.

81. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 80, wherein the final daily dose is from about 7 mg to about 30 mg of Compound A free base.

82. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 81, wherein the final daily dose is from about 8 mg to about 25 mg of Compound A free base.

83. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 79, wherein the final daily dose is about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

84. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 83, wherein the final daily dose is about 10 mg of Compound A free base.

85. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 83, wherein the final daily dose is about 15 mg of Compound A free base.

86. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 83, wherein the final daily dose is about 20 mg of Compound A free base.

87. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 83, wherein the final daily dose is about 25 mg of Compound A free base.

88. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 83, wherein the final daily dose is about 30 mg of Compound A free base.

89. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 88, wherein the initial daily dose is administered QD.

90. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 88, wherein the initial daily dose is administered BID.

91. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 90, wherein the final daily dose is administered QD.

92. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 90, wherein the final daily dose is administered BID.

93. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 88, wherein the initial daily dose and final daily dose are administered QD.

94. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 67 to 93, wherein the titration period is from about 2 to about 14 days.

95. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 94, wherein the titration period is from about 2 to about 7 days.

96. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 95, wherein the titration period is from about 3 to about 7 days.

97. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 94, wherein the titration period is about 2, about 3, about 4, about 5, about 6, or about 7 days.

98. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 2 days.

99. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 3 days.

100. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 4 days.

101. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 5 days.

102. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 6 days.

103. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 97, wherein the titration period is about 7 days.

104. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is about 10 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

105. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is about 15 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

106. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is 20 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

107. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dose in the final dose period is 25 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

108. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 5 mg of Compound A free base, wherein the final daily dosein the final dose period is 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

109. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is about 15 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

110. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is 20 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

111. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is 25 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

112. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration schemecomprises a titration period and a final dose period, wherein the daily dose in the titration period is about 10 mg of Compound A free base, wherein the final daily dose in the final dose period is 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

113. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises a titration period and a final dose period, wherein the daily dose in the titration period is about 20 mg of Compound A free base, wherein the final daily dose in the final dose period is 30 mg of Compound A free base, and wherein the titration period is from about 3 to about 7 days.

114. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 113, wherein the titration period is about 3 days.

115. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 113, wherein the titration period is about 4 days.

116. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 113, wherein the titration period is about 5 days.

117. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 113, wherein the titration period is about 6 days.

118. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 113, wherein the titration period is about 7 days.

119. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 118, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered QD.

120. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 104 to 118, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered BID.

121. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose, during a first titration period, administration of an increased daily dose during a second titration period, and administration at a final daily dose in a final dose period.

122. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 121, wherein the initial daily dose is an amount equivalent to from about 10% to about 30% of the final daily dose.

123. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 122, wherein the initial daily dose is an amount equivalent to about 10% of the final daily dose.

124. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 122, wherein the initial daily dose is an amount equivalent to about 15% of the final daily dose.

125. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 122, wherein the initial daily dose is an amount equivalent to about 20% of the final daily dose.

126. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 122, wherein the initial daily dose is an amount equivalent to about 25% of the final daily dose.

127. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 122, wherein the initial daily dose is an amount equivalent to about 30% of the final daily dosage.

128. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 121 to 127, wherein the initial daily dose is an amount equivalent to from about 2.5 mg to about 10 mg of Compound A free base.

129. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 128, wherein the initial daily dose is an amount equivalent to about 2.5 mg of Compound A free base.

130. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 128, wherein the initial daily dose is an amount equivalent to about 5 mg of Compound A free base.

131. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 128, wherein the initial daily dose is an amount equivalent to about 7.5 mg of Compound A free base.

132. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 128, wherein the initial daily dose is an amount equivalent to about 10 mg of Compound A free base.

133. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 121 to 132, wherein the increased daily dose is an amount equivalent to from about 20% to about 60% of the final daily dose.

134. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 20% of the final daily dose.

135. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 25% of the final daily dose.

136. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 30% of the final daily dose.

137. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 35% of the final daily dose.

138. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 40% of the final daily dose.

139. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 45% of the final daily dose.

140. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 50% of the final daily dose.

141. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 55% of the final daily dose.

142. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to about 60% of the final daily dose.

143. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 133, wherein the increased daily dose is an amount equivalent to from about 5 mg to about 20 mg of Compound A free base.

144. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 5 mg of Compound A free base.

145. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 7.5 mg of Compound A free base.

146. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 10 mg of Compound A free base.

147. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 12.5 mg of Compound A free base.

148. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 15 mg of Compound A free base.

149. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 17.5 mg of Compound A free base.

150. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 143, wherein the increased daily dose is an amount equivalent to about 20 mg of Compound A free base.

151. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 121 to 150, wherein the final daily dose is equivalent to from about 10 mg to about 70 mg of Compound A free base.

152. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 151, wherein the final daily dose is equivalent to from about 10 mg to about 40 mg of Compound A free base.

153. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 151, wherein the final daily dose is equivalent to from about 7 mg to about 30 mg of Compound A free base.

154. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 151, wherein the final daily dose is equivalent to from about 8 mg to about 25 mg of Compound A free base.

155. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 151, wherein the final daily dose is equivalent to about 10, about 15, about 20, about 25, or about 30 mg of Compound A free base.

156. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 121 to 155, wherein the doses are administered BID.

157. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 121 to 155, wherein the doses are administered QD.

158. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimencomprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 15 mg of Compound A free base.

159. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 20 mg of Compound A free base.

160. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg of Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 25 mg of Compound A free base.

161. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable saltthereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 5 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 10 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 30 mg of Compound A free base.

162. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 15 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 20 mg of Compound A free base.

163. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration scheme comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 15 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 30 mg of Compound A free base.

164. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 33, wherein the dosing regimen comprises administration of Compound A, or a pharmaceutically acceptable salt thereof, according to an up-titration scheme, wherein the up-titration schemecomprises administration of Compound A, or a pharmaceutically acceptable salt thereof, at an initial daily dose equivalent to about 10 mg Compound A free base, for a first titration period of from about 2 to about 7 days, administration of an increased daily dose equivalent to about 20 mg of Compound A free base, for a second titration period, and administration at a final daily dose equivalent to about 30 mg of Compound A free base.

165. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 158 to 164, wherein the doses are administered BID.

166. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 158 to 164, wherein the doses are administered QD.

167. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 158 to 166, wherein the first titration period is from about 2 to about 14 days.

168. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 167, wherein the first titration period is from about 2 to about 7 days.

169. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 167, wherein the first titration period is about 2, about 3, about 4, about 5, about 6, or about 7 days.

170. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 158 to 169, wherein the second titration period is from about 1 to about 7 days.

171. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 170, wherein the first titration period is about 1, about 2, about 3, about 4, about 5, about 6, or about 7 days.

172. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 158 to 171, wherein the first and second titration period combined is about 14 days.

173. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 2 days, and the second titration period is about 12 days.

174. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 3 days, and the second titration period is about 11 days.

175. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 4 days, and the second titration period is about 10 days.

176. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 5 days, and the second titration period is about 9 days.

177. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 6 days, and the second titration period is about 8 days.

178. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 172, wherein the first titration period is about 7 days, and the second titration period is about 7 days.

179. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is Compound A free base.

180. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of Compound A.

181. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 180, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of Compound A.

182. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 181, wherein the citrate salt of Compound A is crystalline.

183. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 181, wherein the citrate salt of Compound A is Compound A citrate monohydrate, and wherein the molar ratio between Compound A, citric acid, and water is about 1:1:

1.

184. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 183, wherein Compound A citrate monohydrate is crystalline.

185. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A free base.

186. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of cis-Compound A.

187. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 186, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis-Compound A.

188. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 187, wherein the citrate salt of cis-Compound A is crystalline.

189. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 187, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, and wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:

1.

190. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 189, wherein cis-Compound A citrate monohydrate is crystalline.

191. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 187 to 190, wherein the citrate salt of cis-Compound A or cis-Compound A citrate monohydrate has at least one XRPD peak, in terms of 2-theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°.

192. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered orally.

193. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered via an immediate release formulation.

194. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of proceeding claims, wherein the subject is a human.

195. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of proceeding claims, wherein the neurological or psychiatric disease or disorder is schizophrenia.

196. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of proceeding claims, wherein the neurological or psychiatric disease or disorder is bipolar I disorder.

197. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of proceeding claims, wherein the neurological or psychiatric disease or disorder is Alzheimer’s disease psychosis.

198. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of proceeding claims, wherein the neurological or psychiatric disease or disorder is Parkinson’s disease psychosis.

199. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 198, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate; the neurological or psychiatric disease or disorder is schizophrenia; and the daily dose is equivalent to about 10 mg of cis-Compound A free base.

200. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 198, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate; the neurological or psychiatric disease or disorder is bipolar I disorder; and the daily dose is equivalent to about 10 mg of cis-Compound A free base.

201. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 198, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate; the neurological or psychiatric disease or disorder is schizophrenia; and the daily dose is equivalent to about 20 mg of cis-Compound A free base.

202. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 198, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate; the neurological or psychiatric disease or disorder is bipolar I disorder; and the daily dose is equivalent to about 20 mg of cis-Compound A free base.

203. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 199 to 202, wherein cis-Compound A citrate monohydrate is administered once daily (QD).

204. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is tetrabenazine, or a pharmaceutically acceptable salt thereof.

205. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 125 mg of tetrabenazine free base.

206. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 112.5 mg of tetrabenazine free base.

207. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 12.5 mg to about 112.5 mg of tetrabenazine free base.

208. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent toabout 12.5 mg, about 25 mg, about 37.5 mg, about 50 mg, about 62.5 mg, about 75 mg, about 87.5 mg, about 100 mg, or 112.5 mg of tetrabenazine free base.

209. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 12.5 mg of tetrabenazine free base.

210. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 25 mg of tetrabenazine free base.

211. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 37.5 mg of tetrabenazine free base.

212. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of tetrabenazine free base.

213. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 62.5 mg of tetrabenazine free base.

214. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 75 mg of tetrabenazine free base.

215. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 87.5 mg of tetrabenazine free base.

216. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 100 mg of tetrabenazine free base.

217. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204 or 205, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 112.5 mg of tetrabenazine free base.

218. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 204, wherein tetrabenazine is administered to the subject according to an up-titration scheme.

219. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 218, wherein the up-titration scheme comprises administration of tetrabenazine, or a pharmaceutically acceptable salt thereof, during the titration period, at a titrated daily dose equivalent to about 12.5 mg of tetrabenazine free base for a first period.

220. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 219, wherein the first period, is about 1 week.

221. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 219 or 220, wherein after the first period, the titrated daily dose is increased at weekly intervals by an equivalent to about 12.5 mg of tetrabenazine free base until a daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is reached.

222. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 1 mg to about 125 mg of tetrabenazine free base.

223. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 1 mg to about 112.5 mg of tetrabenazine free base.

224. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to from about 12.5 mg to about 112.5 mg of tetrabenazine free base.

225. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 12.5 mg, about 25 mg, about 37.5 mg, about 50 mg, about 62.5 mg, about 75 mg, about 87.5 mg, about 100 mg, or 112.5 mg of tetrabenazine free base.

226. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 12.5 mg of tetrabenazine free base.

227. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 25 mg of tetrabenazine free base.

228. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, ora pharmaceutically acceptable salt thereof, is equivalent to about 37.5 mg of tetrabenazine free base.

229. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 50 mg of tetrabenazine free base.

230. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 62.5 mg of tetrabenazine free base.

231. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 75 mg of tetrabenazine free base.

232. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 87.5 mg of tetrabenazine free base.

233. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 100 mg of tetrabenazine free base.

234. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 221, wherein the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 112.5 mg of tetrabenazine free base.

235. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 204 to 234, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered BID.

236. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 204 to 234, the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered TID.

237. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 204 to 236, wherein if the daily dose of tetrabenazine, or a pharmaceutically acceptable salt thereof, is equivalent to about 37.5 mg of tetrabenazine free base or greater, then the daily dose of tetrabenazine (tetrabenazine), or a pharmaceutically acceptable salt thereof, is divided into three doses (i.e., TID) with a maximum single dose not to exceed about 25 mg.

238. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 237, wherein the three doses are administered substantially 8 hours apart.

239. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 204 to 238, wherein tetrabenazine is a free base.

240. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 204 to 239, wherein tetrabenazine, or a pharmaceutically acceptable salt thereof, is administered orally.

241. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (I):, or a pharmaceutically acceptable salt thereof, wherein: R1is: a) -C(=O)-O-alkyl; or b) -C(=O)-C1-C6-alkanediyl-NH2, wherein said C1-C6-alkanediyl is optionally substituted with a group selected from: -NH-C(=NH)NH2, -CO2H, -CO2Me, -SH, -C(O)NH2, -NH2, -SCH3, phenyl, - OH, 4-hydroxy-phenyl, imidazolyl, and indolyl.

242. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 241, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (I-A):, or a pharmaceutically acceptable salt thereof.

243. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 241 or 242, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound C (valbenazine):,or a pharmaceutically acceptable salt thereof.

244. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 1 mg to about 100 mg of Compound C free base.

245. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 10 mg to about 100 mg of Compound C free base.

246. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg, or about 100 mg of Compound C free base.

247. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, or about 80 mg of Compound C free base.

248. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg of Compound C free base.

249. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 20 mg of Compound C free base.

250. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 30 mg of Compound C free base.

251. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 40 mg of Compound C free base.

252. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of Compound C free base.

253. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 60 mg of Compound C free base.

254. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 70 mg of Compound C free base.

255. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 243, wherein Compound C (valbenazine), or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 80 mg of Compound C free base.

256. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 241 to 245, wherein the pharmaceutically acceptable salt is a ditosylate salt.

257. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 241 to 246, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound C-Tosylate with the following structure:.

258. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 241 to 247, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

259. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (II):, or a pharmaceutically acceptable salt thereof, wherein: R2is: a) hydrogen; b) -P(=O)(OR3)2; c) -C(=O)alkyl, wherein alkyl is optionally substituted with R4and / or R5; d) -C(=O)heterocyclyl, wherein heterocyclyl is optionally substituted with R4and / or R5;e) -C(=O)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; f) -C(=O)N(R3)alkyl, wherein alkyl is optionally substituted with R4and / or R5; g) -C(=O)N(R3)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; h) -C(=O)Oalkyl, wherein alkyl is optionally substituted with R4and / or R5; or i) alkyl, wherein alkyl is optionally substituted with R4and / or R5; and wherein, each R3is independently hydrogen or alkyl; each R4is independently halo, haloalkyl, cyano, nitro, trimethylsilanyl, –OR7, –SR7, OC(O)R7, N(R7)2, C(O)R7, C(O)OR7, C(O)N(R7)2, N(R7)C(O)OR8, N(R7)C(O)R8, N(R7)C(=NR8)N(R9)2, N(R7)S(O)tR8(wherein t is 1 to 2), S(O)tOR7(where t is 1 to 2), S(O)pR7(where p is 0 to 2) or S(O)tN(R7)2 (where t is 1 to 2), – OP(=O)(OR7)2, or when a single atom bears two R4groups such two R4groups may be taken together to form oxo; each R5is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, or when a single atom bears two R5groups such two R5groups may be taken together to form cycloalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4and / or R6; each R6is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4; and each R7, R8, and R9is independently hydrogen or alkyl.

260. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 259, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (II-A):, or a pharmaceutically acceptable salt thereof.

261. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 259 or 260, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is [(2R,3S,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]methanol, or a pharmaceutically acceptable salt thereof.

262. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 259 or 260, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound D-HCl with the following chemical structure:.

263. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 259 to 262, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

264. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 259 to 263, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

265. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (III):, or a pharmaceutically acceptable salt thereof, wherein: R10and R11are independently lower alkyl, lower cycloalkyl, or lower cycloalkylalkyl, wherein each lower alkyl, lower cycloalkyl, and lower cycloalkylalkyl is independently unsubstituted or substituted with one or more halo, cyano, or lower alkoxy; R12is lower alkyl; and R13is lower alkyl or lower cycloalkylalkyl.

266. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 265, wherein R13is cyclopropyl, cyclobutyl, or - CH2-cyclobutyl.

267. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 265, wherein R13is iso-butyl or neo-pentyl.

268. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of anyone of claims 265 to 267, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (III-B):, or a pharmaceutically acceptable salt thereof.

269. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 265, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (3R,11bS)-3-(2,2-dimethylpropyl)-10-methoxy-2- methyl-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-piperazino[2,1- a]isoquinoline (Compound E), or a pharmaceutically acceptable salt thereof.

270. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 265, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (3R,11bS)-3-(2,2-dimethylpropyl)-10-methoxy-2- methyl-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-piperazino[2,1- a]isoquinoline (Compound F), or a pharmaceutically acceptable salt thereof.

271. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 270, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is an HCl salt.

272. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 271, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

273. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 5 mg to about 150 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

274. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to from about 10 mg to about 100 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

275. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicularmonoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, or about 80 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

276. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 20 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

277. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 30 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

278. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 40 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

279. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 50 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

280. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 60 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

281. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 272, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 70 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

282. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 281, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered at a daily dose equivalent to about 80 mg of the vesicular monoamine transporter 2 (VMAT2) inhibitor free base.

283. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 265 to 282, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

284. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IV):, or a pharmaceutically acceptable salt thereof, wherein: R14is R15, -(CH2)m-R16, or -(CH2)n-OR17; R15is C2-C4alkenyl, C1-C6alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R18; each R18is independently selected from the group consisting of: C1-C4alkoxy, C1-C4alkyl, C1-C4alkylamino, C1-C4alkylsulfonyl, C2-C4dialkylamino, C2- C4dialkylsulfamoyl, halogen, haloC1-C4alkoxy, haloC1-C4alkyl, haloC2- C4dialkylamino, 4-7 membered heterocyclyl, -CN, -OH, and oxo;R16is aryl, C3-C8cycloalkyl, 5-10 membered heteroaryl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R19; each R19is independently selected from the group consisting of: C1-C4alkyl, C1-C4alkylsulfonyl, C1-C4alkylsulfonyloxy, -CN, -CH2CN, halogen, haloC1-C4alkyl, haloC1-C4alkylsulfonyl, oxo, and -OH; R17is C1-C4alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R20; each R20is independently -CN or C3-C6cycloalkyl; m is 0, 1, 2, 3, or 4; and n is 1, 2, or 3.

285. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IV-A):, or a pharmaceutically acceptable salt thereof.

286. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-10- methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-1), or a pharmaceutically acceptable salt thereof.

287. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-(2,2-difluoroethoxy)-3-(2,2- dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound IV-2), or a pharmaceutically acceptable salt thereof.

288. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-(2,2-difluoropropoxy)-3-(2,2- dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound IV-3), or a pharmaceutically acceptable salt thereof.

289. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-cyclopropoxy-3-(2,2- dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound IV-4), or a pharmaceutically acceptable salt thereof.

290. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-10- methoxy-9-(oxetan-3-yloxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound IV-5), or a pharmaceutically acceptable salt thereof.

291. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-9-[(1- fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-6), or a pharmaceutically acceptable salt thereof.

292. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-9-(2- hydroxy-2-methylpropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-7), or a pharmaceutically acceptable salt thereof.

293. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-10- methoxy-9-[(2R)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound IV-8), or a pharmaceutically acceptable salt thereof.

294. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-10- methoxy-9-[(2S)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound IV-9), or a pharmaceutically acceptable salt thereof.

295. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-(3,3-difluoro-2-hydroxypropoxy)- 3-(2,2-dimethylpropyl)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound IV-10), or a pharmaceutically acceptable salt thereof.

296. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-9-[(2R)-2- hydroxypropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound IV-11), or a pharmaceutically acceptable salt thereof.

297. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 284 or 285, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(2,2-dimethylpropyl)-9-[(2S)-2- hydroxypropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound IV-12), or a pharmaceutically acceptable salt thereof.

298. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 284 to 297, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

299. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 284 to 298, wherein the vesicularmonoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

300. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (V):, or a pharmaceutically acceptable salt thereof, wherein: R21is selected from: C3-C7-cycloalkyl-C1-C4-alkylene, C1-C6-alkyl, C3-C7- cycloalkyl, C1-C4-alkyl-O-C2-C4-alkylene, C3-C7-cycloalkyl-O-C2-C4-alkylene, 3-7- membered-heterocyclyl, 3-7-membered-heterocyclyl-C1-C4-alkylene, C4-C8- bicycloalkyl-C1-C4-alkylene, C4-C7-cycloalkenyl, 5-11-membered-spiro-heterocyclyl, C5-C11-spiro-cycloalkyl, cubanyl-C1-C4-alkylene, and 4-8-membered-heterobicyclyl- C1-C4-alkylene; wherein each R21group is optionally substituted with one or more substituents selected from: cyano-C1-C4-alkylene, halogen, C1-C4-alkyl, C1-C4-haloalkyl, cyano, C1-C4-alkylsulfonyl, C3-C6-cycloalkyl, hydroxyl, C1-C4-alkoxy, and C2-C4- dialkylamino.

301. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (V-A):, or a pharmaceutically acceptable salt thereof.

302. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9,10-dimethoxy- 1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-1), or a pharmaceutically acceptable salt thereof.

303. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(2,2- difluoropropoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin- 2-ol (Compound V-2), or a pharmaceutically acceptable salt thereof.

304. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-9- (2,2,2-trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-3), or a pharmaceutically acceptable salt thereof.

305. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-9- (3,3,3-trifluoropropoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-4), or a pharmaceutically acceptable salt thereof.

306. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-cyclopropoxy-10- methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V- 5), or a pharmaceutically acceptable salt thereof.

307. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-((1-fluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-6), or a pharmaceutically acceptable salt thereof.

308. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-ethoxy-10- methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V- 7), or a pharmaceutically acceptable salt thereof.

309. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9- (cyclopropylmethoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-8), or a pharmaceutically acceptable salt thereof.

310. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(3- fluoropropoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2- ol (Compound V-9), or a pharmaceutically acceptable salt thereof.

311. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(ethoxy-d5)-10- methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V- 10), or a pharmaceutically acceptable salt thereof.

312. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(2,2- difluoroethoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2- ol (Compound V-11), or a pharmaceutically acceptable salt thereof.

313. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-9- (4,4,4-trifluorobutoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-12), or a pharmaceutically acceptable salt thereof.

314. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-((3,3- difluorocyclobutyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-13), or a pharmaceutically acceptable salt thereof.

315. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(((S)-2,2- difluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-14), or a pharmaceutically acceptable salt thereof.

316. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(((R)-2,2- difluorocyclopropyl)methoxy)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-15), or a pharmaceutically acceptable salt thereof.

317. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-10-methoxy-9- (methoxy-d3)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound V-16), or a pharmaceutically acceptable salt thereof.

318. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 300 or 301, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(cyclopropylmethoxy-d2)-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1- a]isoquinolin-2-ol (Compound V-17), or a pharmaceutically acceptable salt thereof.

319. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 300 or 318, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

320. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 300 or 319, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

321. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VI):, or a pharmaceutically acceptable salt thereof, wherein: R22is selected from: 3-7-membered-heterocyclyl, 3-7-membered-heterocyclyl- C1-C4-alkylene, 4-8-membered-heterobicyclyl-C1-C4-alkylene, C1-C4-alkyl-O-C2-C4- alkylene, C1-C6-alkyl, C3-C7-cycloalkyl, C3-C7-cycloalkyl-C1-C4-alkylene, C3-C7- cycloalkyl-O-C2-C4-alkylene, C4-C8-bicycloalkyl-C1-C4-alkylene, and C5-C11-spiro- cycloalkyl; wherein each R22group is optionally substituted with one or more substituents selected from: C1-C4-alkoxy, C1-C4-alkyl, C1-C4-haloalkyl, cyano, halogen, and hydroxyl; and R23is halogen.

322. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VI-A):, or a pharmaceutically acceptable salt thereof.

323. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9-[(2R)-2- fluoropropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-1), or a pharmaceutically acceptable salt thereof.

324. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9-[(2S)-2- fluoropropoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-2), or a pharmaceutically acceptable salt thereof.

325. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is cis-(2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9-[(2- fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-3), or a pharmaceutically acceptable salt thereof.

326. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- (((1R,2R)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-4), or a pharmaceutically acceptable salt thereof.

327. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- (((1S,2S)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-5), or a pharmaceutically acceptable salt thereof.

328. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is trans-(2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- [(2-fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-6), or a pharmaceutically acceptable salt thereof.

329. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- (((1R,2S)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-7), or a pharmaceutically acceptable salt thereof.

330. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- (((1S,2R)-2-fluorocyclopropyl)methoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-8), or a pharmaceutically acceptable salt thereof.

331. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-{[(1R)-2,2- difluorocyclopropyl]methoxy}-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-9), or a pharmaceutically acceptable salt thereof.

332. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10- methoxy-9-[(1r,3r)-3-fluorocyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-10), or a pharmaceutically acceptable salt thereof.

333. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-{[(1S)-2,2- difluorocyclopropyl]methoxy}-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol Compound VI-11), or a pharmaceutically acceptable salt thereof.

334. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10- methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-12), or a pharmaceutically acceptable salt thereof.

335. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10- methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-13), or a pharmaceutically acceptable salt thereof.

336. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(2,2- difluoropropoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-14), or a pharmaceutically acceptable salt thereof.

337. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(2,2- difluoroethoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-15), or a pharmaceutically acceptable salt thereof.

338. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9,10- dimethoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-16), or a pharmaceutically acceptable salt thereof.

339. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-{[1- (difluoromethyl)cyclopropyl]methoxy}-8-fluoro-10-methoxy- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-17), or a pharmaceutically acceptable salt thereof.

340. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9-(2- fluoroethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-18), or a pharmaceutically acceptable salt thereof.

341. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-(2H5)ethoxy-8- fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-19), or a pharmaceutically acceptable salt thereof.

342. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is 2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9-[(1-fluorocyclopropyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-20), or a pharmaceutically acceptable salt thereof.

343. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-[(3,3- difluorocyclobutyl)methoxy]-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-21), or a pharmaceutically acceptable salt thereof.

344. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10- methoxy-9-[(1r,3r)-3-(trifluoromethyl)cyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-22), or a pharmaceutically acceptable salt thereof.

345. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-10- methoxy-9-[(1s,3s)-3-(trifluoromethyl)cyclobutoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-23), or a pharmaceutically acceptable salt thereof.

346. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9- [cyclopropyl(2H2)methoxy]-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-24), or a pharmaceutically acceptable salt thereof.

347. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9-cyclopropoxy-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-25), or a pharmaceutically acceptable salt thereof.

348. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-9- (cyclopropylmethoxy)-8-fluoro-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-26), or a pharmaceutically acceptable salt thereof.

349. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-fluoro-9- (2H3)methoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-27), or a pharmaceutically acceptable salt thereof.

350. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-9-{[1- (difluoromethyl)cyclopropyl]methoxy}-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-28), or a pharmaceutically acceptable salt thereof.

351. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-9- (2H5)ethoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-29), or a pharmaceutically acceptable salt thereof.

352. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-9- [cyclopropyl(2H2)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-30), or a pharmaceutically acceptable salt thereof.

353. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-9- (cyclopropylmethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-31), or a pharmaceutically acceptable salt thereof.

354. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-10- methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-32), or a pharmaceutically acceptable salt thereof.

355. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-10- methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-33), or a pharmaceutically acceptable salt thereof.

356. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-(tert-butoxy)-8-chloro-9-[(1- hydroxycyclobutyl)methoxy]-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-34), or a pharmaceutically acceptable salt thereof.

357. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-ethoxy- 10-methoxy-1H,2H,3H,4,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-35), or a pharmaceutically acceptable salt thereof.

358. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-(3-fluoropropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-36), or a pharmaceutically acceptable salt thereof.

359. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-(2- fluoroethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-37), or a pharmaceutically acceptable salt thereof.

360. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9- (2H5)ethoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-38), or a pharmaceutically acceptable salt thereof.

361. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-{[1- (difluoromethyl)cyclopropyl]methoxy}-10-methoxy-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-39), or a pharmaceutically acceptable salt thereof.

362. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-10- methoxy-9-(2,2,2-trifluoroethoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-40), or a pharmaceutically acceptable salt thereof.

363. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-10- methoxy-9-(3,3,3-trifluoropropoxy)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1- a]isoquinolin-2-ol (Compound VI-41), or a pharmaceutically acceptable salt thereof.

364. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-(2,2- difluoropropoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin- 2-ol (Compound VI-42), or a pharmaceutically acceptable salt thereof.

365. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9-(2,2- difluoroethoxy)-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2- ol (Compound VI-43), or a pharmaceutically acceptable salt thereof.

366. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-9- cyclopropoxy-10-methoxy-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-ol (Compound VI-44), or a pharmaceutically acceptable salt thereof.

367. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-10- methoxy-9-[(2R)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-45), or a pharmaceutically acceptable salt thereof.

368. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 322, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-8-bromo-3-(tert-butoxy)-10- methoxy-9-[(2S)-3,3,3-trifluoro-2-hydroxypropoxy]-1H,2H,3H,4H,6H,7H,11bH- pyrido[2,1-a]isoquinolin-2-ol (Compound VI-46), or a pharmaceutically acceptable salt thereof.

369. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 368, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

370. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 321 or 369, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

371. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VII):, or a pharmaceutically acceptable salt thereof, wherein: A1-A27are independently selected from the group consisting of hydrogen and deuterium; and at least one of A1-A27is deuterium.

372. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 371, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VII-A):, or a pharmaceutically acceptable salt thereof.

373. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 371 or 372, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound G, with the following structure:, or a pharmaceutically acceptable salt thereof.

374. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 373, wherein Compound G, or a pharmaceutically acceptable salt thereof, is d6-tetrabenazine that is a racemic mixture of (R,R)-Compound G and (S,S)-Compound G ((RR,SS)-Compound G), or a pharmaceutically acceptable salt thereof, with the following structures:.

375. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 374, wherein Compound G is a free base.

376. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 375, wherein Compound G is crystalline d6- tetrabenazine ((RR,SS)-Compound G) Form I.

377. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 376, wherein crystalline d6-tetrabenazine ((RR,SS)-Compound G) Form I, has an X-ray diffractogram comprising peaks, interms of 2^, at 6.5±0.2°, 12.2±0.2°, 14.4±0.2°, 22.4±0.2°, and 23.4±0.2°; or a pharmaceutically acceptable salt or hydrate thereof.

378. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 376, crystalline d6-tetrabenazine ((RR,SS)- Compound G) Form I, has deuterium enrichment of no less than about 1% and an X- ray diffractogram comprising peaks, in terms of 2^, at 6.5±0.2°, 12.2±0.2°, 14.4±0.2°, 22.4±0.2°, and 23.4±0.2°; or a pharmaceutically acceptable salt or hydrate thereof.

379. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 376, crystalline d6-tetrabenazine ((RR,SS)- Compound G) Form I, has an X-ray diffractogram comprising peaks, in terms of 2^, at 6.5±0.2°, 10.8±0.2°, 12.2±0.2°, 13.0±0.2°, 14.4±0.2°, 17.1±0.2°, 18.0±0.2°, 21.4±0.2°, 22.4±0.2°, and 23.4±0.2°.

380. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 376, crystalline d6-tetrabenazine ((RR,SS)- Compound G) Form I, has a differential calorimetry trace comprising an endotherm between about 115° C and about 135° C.

381. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 376, crystalline d6-tetrabenazine ((RR,SS)- Compound G) Form I, has a thermogravimetric analysis profile showing about 1.5% weight loss below about 150° C.

382. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 371 to 381, the vesicular monoamine transporter 2 (VMAT2) inhibitor is d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to from about 1 mg to about 100 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base.

383. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)-Compound G) is administered at a daily dose equivalent to from about 6 mg to about 60 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base.

384. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to from about 6 mg to about 54 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base.

385. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 6 mg, about 9 mg, about 12 mg, about 18 mg, about 24 mg, about 30 mg, about 36 mg, about 42 mg, or 48 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base.

386. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 6 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

387. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 9 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

388. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 12 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

389. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 18 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

390. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 24 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

391. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 30 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

392. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 36 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

393. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 42 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

394. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 382, wherein d6-tetrabenazine ((RR,SS)- Compound G) is administered at a daily dose equivalent to about 48 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

395. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 371 to 382, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is d6-tetrabenazine ((RR,SS)- Compound G) and is administered to the subject according to an up-titration scheme.

396. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 395, wherein the up-titration scheme comprises administration of d6-tetrabenazine ((RR,SS)-Compound G), during the titrationperiod, at a titrated daily dose equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base for a first period.

397. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 395 or 396, wherein the first period, is about 1 week.

398. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 395 or 396, wherein after the first period, the titrated daily dose is increased at weekly intervals by an equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)-Compound G) free base until a daily dose of d6- tetrabenazine ((RR,SS)-Compound G) is reached.

399. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 100 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

400. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 60 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

401. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to from about 6 mg to about 54 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

402. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 6 mg, about 9 mg, about 12 mg, about 18 mg, about 24 mg, about 30 mg, about 36 mg, about 42 mg, or 48 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base.

403. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 6 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

404. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 9 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

405. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 12 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

406. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 18 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

407. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 24 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

408. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 30 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

409. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 36 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

410. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 42 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

411. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 398, wherein the daily dose of d6-tetrabenazine R,SS)-Compound G) is equivalent to about 48 mg of d6-tetrabenazine ((RR,SS)- Compound G) free base.

412. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 374 to 411, the daily dose of d6- tetrabenazine ((RR,SS)-Compound G) is administered BID.

413. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 374 to 412, wherein if the daily dose of d6-tetrabenazine ((RR,SS)-Compound G) is equivalent to about 12 mg of d6- tetrabenazine ((RR,SS)-Compound G) free base or greater, then the daily dose of d6- tetrabenazine ((RR,SS)-Compound G), or a pharmaceutically acceptable salt thereof, is divided into two doses (i.e., BID).

414. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 413, wherein the two doses are administered about 12 hours apart.

415. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 371 to 414, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

416. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VIII):, or a pharmaceutically acceptable salt thereof, wherein: E1-E27are independently selected from the group consisting of hydrogen and deuterium; and at least one of E1-E27is deuterium.

417. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 416, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

418. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 416 or 417, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

419. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IX):, or a pharmaceutically acceptable salt thereof, wherein:G1-G19and G21-G29are independently selected from the group consisting of hydrogen and deuterium; G20is selected from the group consisting of hydrogen, deuterium, -C(O)O- alkyl and -C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2,-CO2H, -CO2alkyl, -SH, -C(O)NH2, -NH2, phenyl, -OH, 4-hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of G1-G29is deuterium or contains deuterium.

420. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 419, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IX-E):, or a pharmaceutically acceptable salt thereof.

421. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 419 or 420, wherein the stereochemistry for the compound of Formulae IX and IX-E is 2R,3R,11bR.

422. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 419 or 420, wherein the stereochemistry for the compound of Formulae IX and IX-E is 2S,3R,11bR.

423. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 419 to 422, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

424. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 419 to 423, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

425. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (X):, or a pharmaceutically acceptable salt thereof, J1-J19and J21-J29are independently selected from the group consisting of hydrogen and deuterium; J20is selected from the group consisting of hydrogen, deuterium, -C(O)O-alkyl and -C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2, -CO2H, -C(O)2alkyl, -SH, -C(O)NH2, - NH2, phenyl, -OH, 4-hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of J1-J29is deuterium or contains deuterium.

426. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 425, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (X-B):, or a pharmaceutically acceptable salt thereof.

427. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 425, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (X-E):, or a pharmaceutically acceptable salt thereof.

428. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 425 to 427, wherein the stereochemistry for the compound of Formulae X, X-B, and X-E is 2R,3R,11bR.

429. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 425 to 427, wherein the stereochemistry for the compound of Formulae X, X-B, and X-E is 2S,3R,11bR.

430. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 427, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having the following chemical structure:, or a pharmaceutically acceptable salt thereof.

431. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 425 to 430, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

432. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 425 to 431, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

433. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XI):, or a pharmaceutically acceptable salt thereof, wherein: L1-L29are independently selected from the group consisting of hydrogen and deuterium; and at least one of L1-L29is deuterium.

434. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 433, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XI-A):, or a pharmaceutically acceptable salt thereof.

435. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 433, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound H:, or a pharmaceutically acceptable salt thereof.

436. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 433, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound I:, or a pharmaceutically acceptable salt thereof.

437. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 435 or 436, wherein the vesicular monoaminetransporter 2 (VMAT2) inhibitor is a mixture of Compound H and Compound I, or a pharmaceutically acceptable salt thereof.

438. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 437, wherein the mixture of Compound H and Compound I, or a pharmaceutically acceptable salt thereof, is a racemic mixture.

439. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 433 to 438, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

440. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 433 to 439, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

441. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XII):, or a pharmaceutically acceptable salt thereof, wherein: L30-L56are independently selected from the group consisting of hydrogen and deuterium; and at least one of L30-L56is deuterium.

442. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 441, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XII-A):, or a pharmaceutically acceptable salt thereof.

443. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 442, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a diastereomeric mixture of compounds of Formula (XII-A), or a pharmaceutically acceptable salt thereof.

444. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 441 to 443, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

445. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 441 to 444, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

446. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIII):, or a pharmaceutically acceptable salt thereof,wherein: Q1-Q2and Q21are independently selected from the group consisting of -CH3, - CH2D; -CD2H, and -CD3; Q3-Q20are independently selected from the group consisting of hydrogen and deuterium; and at least one of Q1-Q21is deuterium or contains deuterium.

447. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound K (Bevantolol), or a pharmaceutically acceptable salt thereof, with the following structure:.

448. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 447, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound L, or a pharmaceutically acceptable salt thereof, with the following structure:.

449. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 446 to 448, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

450. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 446 to 449, wherein the vesicularmonoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

451. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIV):, or a pharmaceutically acceptable salt thereof, wherein: R24is a C2-C10 fluorinated aliphatic radical; R25is a C1-C10 aliphatic radical, or a C3-C10cycloaliphatic radical; R26is hydrogen or a C1-C10aliphatic radical; and R27is hydrogen or a C1-C10 aliphatic radical.

452. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 451, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIV-A):, or a pharmaceutically acceptable salt thereof.

453. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 452, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound M, or a pharmaceutically acceptable salt thereof, with the following structure:.

454. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 452, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound N, or a pharmaceutically acceptable salt thereof, with the following structure:.

455. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 451 to 454, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

456. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 451 to 455, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

457. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XV):, or a pharmaceutically acceptable salt thereof, wherein: R28is a C1-C10fluorinated aliphatic radical; R29is hydrogen or a C1-C10aliphatic radical; and R30is hydrogen or a C1-C10aliphatic radical.

458. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 457, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XV-A):, or a pharmaceutically acceptable salt thereof.

459. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 457 or 458, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound O, or a pharmaceutically acceptable salt thereof, with the following structure:.

460. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 457 to 459, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

461. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 457 to 460, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

462. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVI):, or a pharmaceutically acceptable salt thereof, wherein: R31is a C1-C10 fluorinated aliphatic radical; R32is hydrogen or a C1-C10 aliphatic radical; R33is hydrogen or a C1-C10 aliphatic radical; and R34is hydrogen, a C1-C10aliphatic radical, a C3-C10cycloaliphatic radical, or a C3-C10aromatic radical.

463. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 462, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVI-A):, or a pharmaceutically acceptable salt thereof.

464. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 462 or 463, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound P, or a pharmaceutically acceptable salt thereof, with the following structure:.

465. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 462 to 464, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

466. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 462 to 465, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

467. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVII):, or a pharmaceutically acceptable salt thereof, wherein: R35is a C1-C10 fluorinated aliphatic radical; R36is a C1-C10 aliphatic radical; R37is hydrogen or a C1-C10aliphatic radical; R38is hydrogen or a C1-C10aliphatic radical; and R39is hydrogen, a C1-C10aliphatic radical, a C2-C10cycloaliphatic radical, or a C2- C20 aromatic radical.

468. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 467, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVII-A):, or a pharmaceutically acceptable salt thereof.

469. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 467 or 468, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVII-B):, or a pharmaceutically acceptable salt thereof.

470. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 467 or 468, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound R, or a pharmaceutically acceptable salt thereof, with the following structure:.

471. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 467 or 468, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound S, or a pharmaceutically acceptable salt thereof, with the following structure:.

472. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 467 to 471, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

473. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 467 to 472, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

474. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVIII):, or a pharmaceutically acceptable salt thereof, wherein: R40, R41, R42, R45, and R46are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether;R43and R44, which are attached to one or more positions of at least one carbon atom of the respective rings, are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether; X is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle, wherein each alkyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle may be optionally substituted with at least one substituent; Y is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic, wherein each alkyl, alkenyl, alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic may be optionally substituted with at least one substituent; “---” is a single bond or a double bond; and “---” is an optional bond, when present the bond is a single bond or a double bond.

475. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 474, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound T, or a pharmaceutically acceptable salt thereof, with the following structure:.

476. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 474, wherein the vesicular monoaminetransporter 2 (VMAT2) inhibitor is Compound U, or a pharmaceutically acceptable salt thereof, with the following structure:.

477. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 474, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound V, or a pharmaceutically acceptable salt thereof, with the following structure:.

478. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 474 to 477, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

479. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 474 to 478, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

480. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIX):, or a pharmaceutically acceptable salt thereof, wherein: “q” is an integer in the range from 1 to 3; “s” is zero or an integer from 1 to 5; R47and R48are each independently an aryl group, wherein R47and R48are each independently unsubstituted or substituted by one or more substituents selected from the group consisting of methyl; deuteromethyl (CD3); tritiomethyl (CT3); ethyl; propyl; isopropyl; C4-C7 straight chain or branched alkyl; C3-C6 cycloalkyl; C4-C7 alkenyl; benzyl; phenylethyl; amino; N-methylamino; N,N-dimethylamino; carboxylate; methylcarboxylate; ethylcarboxylate; propylcarboxylate; isopropylcarboxylate; carboxaldehyde; acetoxy; propionyloxy; isopropionyloxy; cyano; aminomethyl; N-methylaminomethyl; N,N-dimethylaminomethyl; carboxamide; N-methylcarboxamide; N,N-dimethylcarboxamide; acetyl; propionyl; formyl; benzoyl sulfate; phenyl; methylsulfate; hydroxyl; methoxy; ethoxy; propoxy; isopropoxy; thiol; methylthio; ethylthio; propiothiol; fluoro; chloro; bromo; iodo; trifluoromethyl; vinyl; allyl; propargyl; nitro; carbamoyl; ureido; azido; isocyanate; thioisocyanate; hydroxylamino; nitroso; a saturated or unsaturated hydrocarbon ring; a nitrogen-containing heterocyclic moiety; an oxygen-containing heterocyclic moiety; a sulfur-containing heterocyclic moiety; a selenium-containing heterocyclic moiety; a mixed heterocyclic moiety containing at least two atoms selected from the group consisting of nitrogen, oxygen and sulfur; and ortho, meta or para-substituted benzene; R49is methyl, ethyl, propyl, isopropyl, hydroxymethyl, 2-hydroxyethyl, 1- hyhydroxyethyl, methoxymethyl, 2-methoxyethyl, 1-methoxyethyl, aminomethyl, 2- aminoethyl, 1-aminoethyl, N-methylaminomethyl, 2-N-methylaminoethyl, 1-N- methylaminoethyl, N,N-dimethylaminomethyl, 2- N,N-dimethylaminoethyl, or 1-N,N- dimethylaminoethyl group; and R50is a hydrogen atom or a methyl, ethyl, propyl, or isopropyl group.

481. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 480, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIX-A):, or a pharmaceutically acceptable salt thereof.

482. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 480, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIX-B):, or a pharmaceutically acceptable salt thereof.

483. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 480, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound W, or a pharmaceutically acceptable salt thereof, with the following structure:.

484. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 480, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (S)-Compound W, or a pharmaceutically acceptable salt thereof, with the following structure:.

485. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 480, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (S)-3-(4-methoxyphenyl)-N-(1-phenylpropan-2- yl)propan-1-amine hydrochloride.

486. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 480 to 485, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

487. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 480 to 486, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

488. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XX):, or a pharmaceutically acceptable salt thereof, wherein: R51is -C(O)R52, -(C1-C6alkyl)-C(O)R52, -(C2-C4alkenyl)-C(O)R52, -NH-(C1- C4alkyl), -O-CH2-O-C(O)-(C1-C4alkyl), orR52is -OR53or -NH-CH(-C(O)OH)-R54, R53is -H or -C1-C4alkyl, R54is -C1-C4alkyl, optionally substituted by a phenyl group, and R55is -C(O)OR53.

489. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 488, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XX-A):, or a pharmaceutically acceptable salt thereof.

490. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 488 or 489, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is selected from the following compounds: 4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobutanoic acid (Compound XX-1); (2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enoic acid(Compound XX-2); 8-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-8-oxooctanoic acid (Compound XX-3);5-([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)pyridine-3- carboxylic acid(Compound XX-4); (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl butanedioate (Compound XX-5); (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl (2E)-but-2- enedioate (Compound XX-6); 3-((2R,3R,11bR)-3-isobutyl-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H- pyrido[2,1-a]isoquinolin-2-yl)5-isopropyl pyridine-3,5-dicarboxylate (Compound XX-7); (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl 1-isopropyl (2Z)-but-2- enedioate (Compound XX-8); (2S)-2-[(2E)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]- 3-methylbutanoic acid (Compound XX-9); (2S)-2-[(2E)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]- 3-phenylpropanoic acid (Compound XX-10); (2S)-2-[(2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]- 3-methylbutanoic acid (Compound XX-11); (2S)-2-[(2Z)-4-[[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]-4-oxobut-2-enamido]- 3-phenylpropanoic acid (Compound XX-12); (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl N-ethylcarbamate (Compound XX-13); (2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl N-isopropyl carbamate (Compound XX-14);(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl N-(2- methylpropyl)carbamate (Compound XX-15); [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl propanoate (Compound XX-16); [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl 2-methylpropanoate (Compound XX-17); and [([[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)- 1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]oxy]carbonyl)oxy]methyl 3-methylbutanoate (Compound XX-18); or a pharmaceutically acceptable salt thereof.

491. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 488 to 490, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

492. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 488 to 491, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

493. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXI):,or a pharmaceutically acceptable salt thereof, wherein: R56is a bond, -C1-C8alkyl-, -C2-C4alkenyl-, or .

494. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is 3,5-bis-[(2R,3R,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl]pyridine- 3,5-dicarboxylate (Compound XXI-1), or a pharmaceutically acceptable salt thereof.

495. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is bis-[(2R,3R,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] octanedioate (Compound XXI-2), or a pharmaceutically acceptable salt thereof.

496. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is [(2R,3R,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] butanedioate (Compound XXI-3), or a pharmaceutically acceptable salt thereof.

497. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is bis-[(2R,3R,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] (2E)-but-2- enedioate (Compound XXI-4), or a pharmaceutically acceptable salt thereof.

498. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is bis-[(2R,3R,11bR)-9,10-dimethoxy-3-(2-methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] (2Z)-but-2- enedioate (Compound XXI-5), or a pharmaceutically acceptable salt thereof.

499. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 493, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is bis[(2R,3R,11bR)-9,10-dimethoxy-3-(2- methylpropyl)-1H,2H,3H,4H,6H,7H,11bH-pyrido[2,1-a]isoquinolin-2-yl] oxalate (Compound XXI-6), or a pharmaceutically acceptable salt thereof.

500. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 493 to 499, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

501. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 493 to 500, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

502. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXII):, or a pharmaceutically acceptable salt thereof, wherein: R57is C1-C4alkyl and is optionally substituted with one or more deuterium atoms; W is18F or19F; and Y is -(CRaRb)r-, wherein Raand Rbare each independently hydrogen or deuterium atoms, “r” is an integer from 1 to 6; provided that at least one deuterium atom is present at either R57or Y; andprovided that when “r” is 2, R57is not CH3.

503. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 502, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXII-A):, or a pharmaceutically acceptable salt thereof.

504. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 502, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXII-B):, or a pharmaceutically acceptable salt thereof.

505. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 502 to 504, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

506. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 502 to 505, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

507. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXIII):, or a pharmaceutically acceptable salt thereof, wherein: X1is a substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl; Z is N or CH; “w” is 1, 2, or 3; “Ar” is substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl; R58is H, ethyl ester, isopropyl ester, -C(O)-alkyl (i.e., methyl ketone, ethyl ketone, etc.), or substituted or unsubstituted 5-membered heteroaryl; and R59is H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; wherein the bond between the carbon atoms bearing “Ar” and R58is a single or double bond.

508. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 507, wherein R59is H, X2and X3are H, and X4and X5are independently H, fluoro, or trifluoromethyl.

509. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 507 or 508, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

510. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 507 to 509, wherein the vesicularmonoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

511. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 1 to 203, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXIV):, or a pharmaceutically acceptable salt thereof, wherein: “---” represents: a single bond or a double bond; when “---” is a single bond, R60is selected from OH, H, orwhen “---” is a double bond, R60is O; R61is selected from hydrogen, methyl, or ethyl; R62is selected from C2-C10alkyl, C3-C6cycloalkyl, C3-C6cycloalkyl-C1- C6alkyl, 3- to 6-membered heterocycloalkyl-C1-C3alkyl, C2-C6alkenyl or C1- C6heteroalkyl unsubstituted, or substituted with 1, 2, or 3 R63groups; and R63is selected from F, Cl, Br, OH, SH, or NH2.

512. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-isobutyl-10-methoxy-9-(2,2,2- trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-1), or a pharmaceutically acceptable salt thereof.

513. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoaminetransporter 2 (VMAT2) inhibitor is (2S,3S,11bS)-3-isobutyl-10-methoxy-9-(2,2,2- trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-2), or a pharmaceutically acceptable salt thereof.

514. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-3-isobutyl-10-methoxy-9-(2,2,2- trifluoroethoxy)-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-yl L-valinate (Compound XXIV-3), or a pharmaceutically acceptable salt thereof.

515. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-(cyclopropylmethoxy)-3- isobutyl-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-4), or a pharmaceutically acceptable salt thereof.

516. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2S,3S,11bS)-9-(cyclopropylmethoxy)-3-isobutyl- 10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-ol (Compound XXIV-5), or a pharmaceutically acceptable salt thereof.

517. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of claim 511, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is (2R,3R,11bR)-9-(cyclopropylmethoxy)-3- isobutyl-10-methoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1-a]isoquinolin-2-yl L- valinate (Compound XXIV-6), or a pharmaceutically acceptable salt thereof.

518. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 511 to 517, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a free base.

519. The method, the compound, the use, the VMAT2 inhibitor, the multi-pack, or the pharmaceutical composition of any one of claims 511 to 518, wherein the vesicularmonoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, is administered orally.

520. The method, the compound, or the use of any one of the preceding claims wherein before administration of Compound A, or a pharmaceutically acceptable salt thereof, either the subject or a medical care worker is informed that the administration may result in an adverse reaction selected from somnolence, sedation, fatigue, and lethargy.

521. The method, the compound, or the use of claim 520, wherein the adverse reaction is somnolence.

522. The method, the compound, or the use of claim 520, further comprising informing the subject or medical care worker that the subject should not perform activities requiring mental alertness.

523. The method, the compound, or the use of claim 520, further comprising informing the subject or medical care worker that the administration may impair judgment, thinking, or motor skills.

524. The method, the compound, or the use of any one of claim 520 to 523, further comprising informing the subject or medical care worker that the administration may impair the subject’s ability to perform tasks that require complex motor skills and mental skills.

525. The method, the compound, or the use of any one of claim 520 to 524, further comprising informing the subject or medical care worker that the administration may cause slow reaction times.

526. The method, the compound, or the use of claim 520 to 525, further comprising informing the subject or medical care worker that the administration may impair the subject’s ability to drive or operate hazardous machinery.

527. The method, the compound, or the use of claim 520 to 526, further comprising cautioning the subject about operating hazardous machinery.

528. The method, the compound, or the use of any one of the preceding claims wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered with or without food.

529. The method, the compound, or the use of claim 528, wherein said administration results in no significant food effect.

530. The method, the compound, or the use of any one of the preceding claims, wherein said Compound A, or a pharmaceutically acceptable salt thereof, is administered to a subject who is in a fed or fasted state.

531. The method, the compound, or the use of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered with food.

532. The method, the compound, or the use of any one of the preceding claims, wherein Compound A, or a pharmaceutically acceptable salt thereof, is administered without food.

533. A pharmaceutical composition for comprising a compound having the structure:, or a pharmaceutically acceptable salt thereof, and a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

534. A combination comprising a unit dosage form of Compound A:, or a pharmaceutically acceptable salt thereof, and a separate unit dosage form of a vesicular monoamine transporter 2 (VMAT2) inhibitor, or a pharmaceutically acceptable salt thereof, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 80 mg of Compound A free base.

535. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 70 mg of Compound A free base.

536. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 5 mg to about 70 mg of Compound A free base.

537. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 40 mg of Compound A free base.

538. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 5 mg to about 40 mg of Compound A free base.

539. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 10 mg to about 40 mg of Compound A free base.

540. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 30 mg of Compound A free base.

541. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 7 mg to about 30 mg of Compound A free base.

542. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 25 mg of Compound A free base.

543. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 8 mg to about 25 mg of Compound A free base.

544. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 2.5 mg to about 20 mg of Compound A free base.

545. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to from about 5 mg to about 20 mg of Compound A free base.

546. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 2.5 mg, about 5 mg, about 7.5 mg, about 10 mg, about 12.5 mg, about 15 mg, about 17.5 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

547. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 2.5 mg, about 5 mg, about 7.5 mg, about 10 mg, about 12.5 mg, about 15 mg, about 17.5 mg, or about 20 mg of Compound A free base.

548. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily doseequivalent to about 10 mg, about 15 mg, about 20 mg, about 25 mg, or about 30 mg of Compound A free base.

549. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 2.5 mg of Compound A free base.

550. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 5 mg of Compound A free base.

551. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 7.5 mg of Compound A free base.

552. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 10 mg of Compound A free base.

553. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 12.5 mg of Compound A free base.

554. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 15 mg of Compound A free base.

555. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 17.5 mg of Compound A free base.

556. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 20 mg of Compound A free base.

557. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 25 mg of Compound A free base.

558. The pharmaceutical composition or the combination of claim 533 or 534, wherein the Compound A, or a pharmaceutically acceptable salt thereof, is at a daily dose equivalent to about 30 mg of Compound A free base.

559. The pharmaceutical composition or the combination of any one of claims 533 to 558, wherein Compound A, or a pharmaceutically acceptable salt thereof, is Compound A free base.

560. The pharmaceutical composition or the combination of any one of claims 534 to 558, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of Compound A.

561. The pharmaceutical composition or the combination of claim 560, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of Compound A.

562. The pharmaceutical composition or the combination of claim 561, wherein the citrate salt of Compound A is crystalline.

563. The pharmaceutical composition or the combination of claim 561, wherein the citrate salt of Compound A is Compound A citrate monohydrate, and wherein the molar ratio between Compound A, citric acid, and water is about 1:1:

1.

564. The pharmaceutical composition or the combination of claim 563, wherein Compound A citrate monohydrate is crystalline.

565. The pharmaceutical composition or the combination of any one of claims 533 to 564, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis- Compound A free base.

566. The pharmaceutical composition or the combination of any one of claims 533 to 564, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a pharmaceutically acceptable salt of cis-Compound A.

567. The pharmaceutical composition or the combination of claim 566, wherein Compound A, or a pharmaceutically acceptable salt thereof, is a citrate salt of cis- Compound A.

568. The pharmaceutical composition or the combination of claim 567, wherein the citrate salt of cis-Compound A is crystalline.

569. The pharmaceutical composition or the combination of claim 567, wherein Compound A, or a pharmaceutically acceptable salt thereof, is cis-Compound A citrate monohydrate, and wherein the molar ratio between cis-Compound A, citric acid, and water is about 1:1:

1.

570. The pharmaceutical composition or the combination of claim 569, wherein cis- Compound A citrate monohydrate is crystalline.

571. The pharmaceutical composition or the combination of any one of claims 567 to 570, wherein the citrate salt of cis-Compound A or cis-Compound A citrate monohydrate has at least one XRPD peak, in terms of 2-theta, selected from 11.3°± 0.2°, 18.4°± 0.2°, 19.2°± 0.2°, and 20.5°± 0.2°.

572. The pharmaceutical composition or the combination of any one of claims 533 to 571, wherein Compound A, or a pharmaceutically acceptable salt thereof, is formulated for administered orally.

573. The pharmaceutical composition or the combination of any one of claims 533 to 572, wherein Compound A, or a pharmaceutically acceptable salt thereof, is formulated for immediate release formulation.

574. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is tetrabenazine, or a pharmaceutically acceptable salt thereof.

575. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (I):, or a pharmaceutically acceptable salt thereof, wherein: R1is: a) -C(=O)-O-alkyl; or b) -C(=O)-C1-C6-alkanediyl-NH2, wherein said C1-C6-alkanediyl is optionally substituted with a group selected from: -NH-C(=NH)NH2, -CO2H, -CO2Me, -SH, -C(O)NH2, -NH2, -SCH3, phenyl, - OH, 4-hydroxy-phenyl, imidazolyl, and indolyl.

576. The pharmaceutical composition or the combination of claim 575, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (I-A):, or a pharmaceutically acceptable salt thereof.

577. The pharmaceutical composition or the combination of claim 575, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound C (valbenazine):, or a pharmaceutically acceptable salt thereof.

578. The pharmaceutical composition or the combination of claim 575, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound C-Tosylate with the following structure:.

579. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (II):, or a pharmaceutically acceptable salt thereof, wherein: R2is:a) hydrogen; b) -P(=O)(OR3)2; c) -C(=O)alkyl, wherein alkyl is optionally substituted with R4and / or R5; d) -C(=O)heterocyclyl, wherein heterocyclyl is optionally substituted with R4and / or R5; e) -C(=O)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; f) -C(=O)N(R3)alkyl, wherein alkyl is optionally substituted with R4and / or R5; g) -C(=O)N(R3)carbocyclyl, wherein carbocyclyl is optionally substituted with R4and / or R5; h) -C(=O)Oalkyl, wherein alkyl is optionally substituted with R4and / or R5; or i) alkyl, wherein alkyl is optionally substituted with R4and / or R5; and wherein, each R3is independently hydrogen or alkyl; each R4is independently halo, haloalkyl, cyano, nitro, trimethylsilanyl, –OR7, –SR7, OC(O)R7, N(R7)2, C(O)R7, C(O)OR7, C(O)N(R7)2, N(R7)C(O)OR8, N(R7)C(O)R8, N(R7)C(=NR8)N(R9)2, N(R7)S(O)tR8(wherein t is 1 to 2), S(O)tOR7(where t is 1 to 2), S(O)pR7(where p is 0 to 2) or S(O)tN(R7)2(where t is 1 to 2), – OP(=O)(OR7)2, or when a single atom bears two R4groups such two R4groups may be taken together to form oxo; each R5is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, or when a single atom bears two R5groups such two R5groups may be taken together to form cycloalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4and / or R6; each R6is independently alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl or heteroarylalkyl, wherein each of said alkyl, alkenyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heterocyclyl, heterocyclalkyl, heteroaryl and heteroarylalkyl groups is optionally substituted with R4; and each R7, R8, and R9is independently hydrogen or alkyl.

580. The pharmaceutical composition or the combination of claim 579, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (II-A):, or a pharmaceutically acceptable salt thereof.

581. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (III):, or a pharmaceutically acceptable salt thereof, wherein: R10and R11are independently lower alkyl, lower cycloalkyl, or lower cycloalkylalkyl, wherein each lower alkyl, lower cycloalkyl, and lower cycloalkylalkyl is independently unsubstituted or substituted with one or more halo, cyano, or lower alkoxy; R12is lower alkyl; and R13is lower alkyl or lower cycloalkylalkyl.

582. The pharmaceutical composition or the combination of claim 581, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (III-B):, or a pharmaceutically acceptable salt thereof.

583. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IV):, or a pharmaceutically acceptable salt thereof, wherein: R14is R15, -(CH2)m-R16, or -(CH2)n-OR17; R15is C2-C4alkenyl, C1-C6alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R18; each R18is independently selected from the group consisting of: C1-C4alkoxy, C1-C4alkyl, C1-C4alkylamino, C1-C4alkylsulfonyl, C2-C4dialkylamino, C2- C4dialkylsulfamoyl, halogen, haloC1-C4alkoxy, haloC1-C4alkyl, haloC2- C4dialkylamino, 4-7 membered heterocyclyl, -CN, -OH, and oxo; R16is aryl, C3-C8cycloalkyl, 5-10 membered heteroaryl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R19; each R19is independently selected from the group consisting of: C1-C4alkyl, C1-C4alkylsulfonyl, C1-C4alkylsulfonyloxy, -CN, -CH2CN, halogen, haloC1-C4alkyl, haloC1-C4alkylsulfonyl, oxo, and -OH; R17is C1-C4alkyl, C3-C8cycloalkyl, or 4-7 membered heterocyclyl, each unsubstituted or substituted with one or more R20; each R20is independently -CN or C3-C6cycloalkyl; m is 0, 1, 2, 3, or 4; and n is 1, 2, or 3.

584. The pharmaceutical composition or the combination of claim 583, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IV-A):, or a pharmaceutically acceptable salt thereof.

585. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (V):, or a pharmaceutically acceptable salt thereof, wherein: R21is selected from: C3-C7-cycloalkyl-C1-C4-alkylene, C1-C6-alkyl, C3-C7- cycloalkyl, C1-C4-alkyl-O-C2-C4-alkylene, C3-C7-cycloalkyl-O-C2-C4-alkylene, 3-7- membered-heterocyclyl, 3-7-membered-heterocyclyl-C1-C4-alkylene, C4-C8- bicycloalkyl-C1-C4-alkylene, C4-C7-cycloalkenyl, 5-11-membered-spiro-heterocyclyl, C5-C11-spiro-cycloalkyl, cubanyl-C1-C4-alkylene, and 4-8-membered-heterobicyclyl- C1-C4-alkylene; wherein each R21group is optionally substituted with one or more substituents selected from: cyano-C1-C4-alkylene, halogen, C1-C4-alkyl, C1-C4-haloalkyl, cyano, C1-C4-alkylsulfonyl, C3-C6-cycloalkyl, hydroxyl, C1-C4-alkoxy, and C2-C4- dialkylamino.

586. The pharmaceutical composition or the combination of claim 585, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (V-A):, or a pharmaceutically acceptable salt thereof.

587. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VI):, or a pharmaceutically acceptable salt thereof, wherein: R22is selected from: 3-7-membered-heterocyclyl, 3-7-membered-heterocyclyl- C1-C4-alkylene, 4-8-membered-heterobicyclyl-C1-C4-alkylene, C1-C4-alkyl-O-C2-C4- alkylene, C1-C6-alkyl, C3-C7-cycloalkyl, C3-C7-cycloalkyl-C1-C4-alkylene, C3-C7- cycloalkyl-O-C2-C4-alkylene, C4-C8-bicycloalkyl-C1-C4-alkylene, and C5-C11-spiro- cycloalkyl; wherein each R22group is optionally substituted with one or more substituents selected from: C1-C4-alkoxy, C1-C4-alkyl, C1-C4-haloalkyl, cyano, halogen, and hydroxyl; and R23is halogen.

588. The pharmaceutical composition or the combination of claim 587, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VI-A):, or a pharmaceutically acceptable salt thereof.

589. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VII):, or a pharmaceutically acceptable salt thereof, wherein: A1-A27are independently selected from the group consisting of hydrogen and deuterium; and at least one of A1-A27is deuterium.

590. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (VIII):, or a pharmaceutically acceptable salt thereof, wherein:E1-E27are independently selected from the group consisting of hydrogen and deuterium; and at least one of E1-E27is deuterium.

591. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (IX):, or a pharmaceutically acceptable salt thereof, wherein: G1-G19and G21-G29are independently selected from the group consisting of hydrogen and deuterium; G20is selected from the group consisting of hydrogen, deuterium, -C(O)O- alkyl and -C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2,-CO2H, -CO2alkyl, -SH, -C(O)NH2, -NH2, phenyl, -OH, 4-hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of G1-G29is deuterium or contains deuterium.

592. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (X):, or a pharmaceutically acceptable salt thereof, J1-J19and J21-J29are independently selected from the group consisting of hydrogen and deuterium; J20is selected from the group consisting of hydrogen, deuterium, -C(O)O-alkyl and -C(O)-C1-C6alkyl, or a group cleavable under physiological conditions, wherein said alkyl or C1-C6alkyl is optionally substituted with one or more substituents selected from the group consisting of -NH-C(NH)NH2, -CO2H, -C(O)2alkyl, -SH, -C(O)NH2, - NH2, phenyl, -OH, 4-hydroxyphenyl, imidazolyl, and indolyl, and any R20substituent is further optionally substituted with deuterium; and at least one of J1-J29is deuterium or contains deuterium.

593. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XI):, or a pharmaceutically acceptable salt thereof, wherein: L1-L29are independently selected from the group consisting of hydrogen and deuterium; and at least one of L1-L29is deuterium.

594. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XII):, or a pharmaceutically acceptable salt thereof, wherein: L30-L56are independently selected from the group consisting of hydrogen and deuterium; and at least one of L30-L56is deuterium.

595. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIII):, or a pharmaceutically acceptable salt thereof, wherein: Q1-Q2and Q21are independently selected from the group consisting of -CH3, - CH2D; -CD2H, and -CD3; Q3-Q20are independently selected from the group consisting of hydrogen and deuterium; and at least one of Q1-Q21is deuterium or contains deuterium.

596. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound K (Bevantolol), or a pharmaceutically acceptable salt thereof, with the following structure:.

597. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIV):, or a pharmaceutically acceptable salt thereof, wherein: R24is a C2-C10 fluorinated aliphatic radical; R25is a C1-C10 aliphatic radical, or a C3-C10 cycloaliphatic radical; R26is hydrogen or a C1-C10 aliphatic radical; and R27is hydrogen or a C1-C10aliphatic radical.

598. The pharmaceutical composition or the combination of claim 597, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIV-A):, or a pharmaceutically acceptable salt thereof.

599. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XV):, or a pharmaceutically acceptable salt thereof, wherein: R28is a C1-C10 fluorinated aliphatic radical; R29is hydrogen or a C1-C10 aliphatic radical; and R30is hydrogen or a C1-C10aliphatic radical.

600. The pharmaceutical composition or the combination of claim 599, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XV-A):, or a pharmaceutically acceptable salt thereof.

601. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVI):, or a pharmaceutically acceptable salt thereof, wherein:R31is a C1-C10fluorinated aliphatic radical; R32is hydrogen or a C1-C10aliphatic radical; R33is hydrogen or a C1-C10 aliphatic radical; and R34is hydrogen, a C1-C10 aliphatic radical, a C3-C10 cycloaliphatic radical, or a C3-C10 aromatic radical.

602. The pharmaceutical composition or the combination of claim 601, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVI-A):, or a pharmaceutically acceptable salt thereof.

603. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVII):, or a pharmaceutically acceptable salt thereof, wherein: R35is a C1-C10fluorinated aliphatic radical; R36is a C1-C10aliphatic radical; R37is hydrogen or a C1-C10aliphatic radical; R38is hydrogen or a C1-C10aliphatic radical; and R39is hydrogen, a C1-C10 aliphatic radical, a C2-C10 cycloaliphatic radical, or a C2- C20aromatic radical.

604. The pharmaceutical composition or the combination of claim 603, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVII-A):, or a pharmaceutically acceptable salt thereof.

605. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XVIII):, or a pharmaceutically acceptable salt thereof, wherein: R40, R41, R42, R45, and R46are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether; R43and R44, which are attached to one or more positions of at least one carbon atom of the respective rings, are independently selected from H, halogen, hydroxyl, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, C1-C8alkoxy, 3- to 8-membered carbocyclic or heterocyclic, aryl, heteroaryl, C1-C4aralkyl, residues of glycolic acid, ethylene glycol / propylene glycol copolymers, carboxylate, ester, amide, carbohydrate, amino acid, alditol, OC(X)2COOH, SC(X)2COOH, NHCHXCOOH, COY, CO2Y, sulfate, sulfonamide, sulfoxide, sulfonate, sulfone, thioalkyl, thioester, propylphthalimide, and thioether;X is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle, wherein each alkyl, carbocycle, aryl, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, and alkylheterocycle may be optionally substituted with at least one substituent; Y is selected from H, C1-C8alkyl, C1-C8alkenyl, C1-C8alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic, wherein each alkyl, alkenyl, alkynyl, aryl, carbocycle, heteroaryl, heterocycle, alkylaryl, alkylheteroaryl, alkylheterocycle, and heteroaromatic may be optionally substituted with at least one substituent; “---” is a single bond or a double bond; and “---” is an optional bond, when present the bond is a single bond or a double bond.

606. The pharmaceutical composition or the combination of claim 605, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is Compound T, or a pharmaceutically acceptable salt thereof, with the following structure:.

607. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XIX):, or a pharmaceutically acceptable salt thereof, wherein: “q” is an integer in the range from 1 to 3; “s” is zero or an integer from 1 to 5;R47and R48are each independently an aryl group, wherein R47and R48are each independently unsubstituted or substituted by one or more substituents selected from the group consisting of methyl; deuteromethyl (CD3); tritiomethyl (CT3); ethyl; propyl; isopropyl; C4-C7straight chain or branched alkyl; C3-C6cycloalkyl; C4-C7alkenyl; benzyl; phenylethyl; amino; N-methylamino; N,N-dimethylamino; carboxylate; methylcarboxylate; ethylcarboxylate; propylcarboxylate; isopropylcarboxylate; carboxaldehyde; acetoxy; propionyloxy; isopropionyloxy; cyano; aminomethyl; N-methylaminomethyl; N,N-dimethylaminomethyl; carboxamide; N-methylcarboxamide; N,N-dimethylcarboxamide; acetyl; propionyl; formyl; benzoyl sulfate; phenyl; methylsulfate; hydroxyl; methoxy; ethoxy; propoxy; isopropoxy; thiol; methylthio; ethylthio; propiothiol; fluoro; chloro; bromo; iodo; trifluoromethyl; vinyl; allyl; propargyl; nitro; carbamoyl; ureido; azido; isocyanate; thioisocyanate; hydroxylamino; nitroso; a saturated or unsaturated hydrocarbon ring; a nitrogen-containing heterocyclic moiety; an oxygen-containing heterocyclic moiety; a sulfur-containing heterocyclic moiety; a selenium-containing heterocyclic moiety; a mixed heterocyclic moiety containing at least two atoms selected from the group consisting of nitrogen, oxygen and sulfur; and ortho, meta or para-substituted benzene; R49is methyl, ethyl, propyl, isopropyl, hydroxymethyl, 2-hydroxyethyl, 1- hyhydroxyethyl, methoxymethyl, 2-methoxyethyl, 1-methoxyethyl, aminomethyl, 2- aminoethyl, 1-aminoethyl, N-methylaminomethyl, 2-N-methylaminoethyl, 1-N- methylaminoethyl, N,N-dimethylaminomethyl, 2- N,N-dimethylaminoethyl, or 1-N,N- dimethylaminoethyl group; and R50is a hydrogen atom or a methyl, ethyl, propyl, or isopropyl group.

608. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XX):, or a pharmaceutically acceptable salt thereof, wherein: R51is -C(O)R52, -(C1-C6alkyl)-C(O)R52, -(C2-C4alkenyl)-C(O)R52, -NH-(C1- C4alkyl), -O-CH2-O-C(O)-(C1-C4alkyl), orR52is -OR53or -NH-CH(-C(O)OH)-R54, R53is -H or -C1-C4alkyl, R54is -C1-C4alkyl, optionally substituted by a phenyl group, and R55is -C(O)OR53.

609. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXI):, or a pharmaceutically acceptable salt thereof, wherein: R56is a bond, -C1-C8alkyl-, -C2-C4alkenyl-, or.

610. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXII):, or a pharmaceutically acceptable salt thereof, wherein: R57is C1-C4alkyl and is optionally substituted with one or more deuterium atoms; W is18F or19F; and Y is -(CRaRb)r-, wherein Raand Rbare each independently hydrogen or deuterium atoms, “r” is an integer from 1 to 6; provided that at least one deuterium atom is present at either R57or Y; and provided that when “r” is 2, R57is not CH3.

611. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXIII):, or a pharmaceutically acceptable salt thereof, wherein: X1is a substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl;Z is N or CH; “w” is 1, 2, or 3; “Ar” is substituted or unsubstituted 5- or 6-membered aryl or substituted or unsubstituted 5- or 6-membered heteroaryl; R58is H, ethyl ester, isopropyl ester, -C(O)-alkyl (i.e., methyl ketone, ethyl ketone, etc.), or substituted or unsubstituted 5-membered heteroaryl; and R59is H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; wherein the bond between the carbon atoms bearing “Ar” and R58is a single or double bond.

612. The pharmaceutical composition or the combination of any one of claims 533 to 573, wherein the vesicular monoamine transporter 2 (VMAT2) inhibitor is a compound having Formula (XXIV):, or a pharmaceutically acceptable salt thereof, wherein: “---” represents: a single bond or a double bond; when “---” is a single bond, R60is selected from OH, H, orwhen “---” is a double bond, R60is O; R61is selected from hydrogen, methyl, or ethyl; R62is selected from C2-C10alkyl, C3-C6cycloalkyl, C3-C6cycloalkyl-C1- C6alkyl, 3- to 6-membered heterocycloalkyl-C1-C3alkyl, C2-C6alkenyl or C1- C6heteroalkyl unsubstituted, or substituted with 1, 2, or 3 R63groups; and R63is selected from F, Cl, Br, OH, SH, or NH2.

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