Combination of dextromethorphan and bupropion for the treatment of depression

Abstract

Dosage forms, drug delivery systems, and methods related to the sustained release of dextromethorphan or enhanced therapeutic effects are disclosed. Typically, bupropion or a related compound is administered orally to a human being treated with or who is being treated with dextromethorphan.

Description

COMBINATION OF DEXTROMETHORPHAN AND BUPROP1ON FOR THE TREATMENT OF DEPRESSION Cross reference to related requests This application claims the benefit of US Provisional Patent Application Nos. 62 / 789,431, filed January 7, 2019; 62 / 789,446, filed January 7, 2019; 62 / 789,451, filed January 7, 2019; and 62 / 789,488, filed January 7, 2019, all of which are incorporated herein by reference in their entireties. Brief description of the invention Some embodiments include a method of increasing dextromethorphan plasma levels in a human, comprising co-administration of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds with dextromethorphan. Some embodiments include a method of increasing dextromethorphan plasma levels in a human, comprising co-administration of erythrohydroxybupropion or a prodrug thereof, with dextromethorphan to the human, wherein the erythrohydroxybupropion or a prodrug thereof is administered in an amount that results in an AUC0-12 of dextromethorphan that is at least about 40 ng"hr / mL. Some embodiments include a method of increasing dextromethorphan plasma levels in a human, comprising co-administration of erythrohydroxybupropion or a prodrug thereof, with dextromethorphan to the human, wherein the erythrohydroxybupropion or a prodrug thereof is administered in an amount that results in a dextromethorphan Cmax that is at least approximately 6 ng / mL. Some embodiments include a method of increasing dextromethorphan plasma levels in a human, comprising co-administration of erythrohydroxybupropion or a prodrug thereof, with dextromethorphan to the human, wherein the erythrohydroxybupropion or a prodrug thereof is administered in an amount that results in a Cmean of dextromethorphan over the period between two independent and consecutive administrations of dextromethorphan that is at least approximately 5 ng / mL. Some embodiments include a method of increasing the metabolic life of dextromethorphan, comprising administering threohydroxybupropion or a drug thereof to a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan and where dextromethorphan it is present in the human body at the same time as threohydroxybupropion. Some modalities include a method of reducing an adverse event associated with dextromethorphan treatment, comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan to a human patient in need of treatment with / ^ζοηη / ίζηζ / Β / γι dextromethorphan, in where the human patient is at risk of experiencing the adverse event as a result of dextromethorphan treatment. Some modalities include a sustained release oral delivery system for dextromethorphan, comprising bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a prodrug of any of these compounds, dextromethorphan, and a water-soluble vehicle. Some modalities include a method of reducing the number of doses of dextromethorphan that can be administered without loss of efficacy, comprising oral administration of an effective amount of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a prodrug of any of these compounds to a human being in need of dextromethorphan treatment. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the threohydroxybupropion or prodrug thereof is administered on the first day of at least two days of dextromethorphan treatment, where a reduction in the plasma dextrorphan level occurs on the first day that threohydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without threohydroxybupropion or a prodrug thereof. same. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the hydroxybupropion or prodrug thereof is administered on the first day of at least two days of dextromethorphan treatment, where a reduction in plasma dextrorphan level occurs on the first day that hydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof. same. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of bupropion and dextromethorphan to a human in need of dextromethorphan treatment, wherein bupropion is administered on the first day of at least two days of dextromethorphan treatment, in where a reduction in plasma dextrorphan level occurs on the first day that bupropion and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without bupropion. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the erythrohydroxybupropion or prodrug thereof is administered on the first day of at least two days of dextromethorphan treatment, where a reduction in the plasma dextrorphan level occurs on the first day that erythrohydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof. same. Some modalities include a method of reducing plasma dextrorphan levels which / ^ζοηη / ίζηζ / Β / γι comprises the co-administration of bupropion and dextromethorphan, for at least eight consecutive days, to a human in need of dextromethorphan treatment, wherein, on the eighth day, the plasma dextrorphan level is less than the plasma dextrorphan level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for eight consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least eight consecutive days, to a human in need of dextromethorphan treatment, wherein, on the eighth day , the dextrorphan plasma level is lower than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for eight consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least eight consecutive days, to a human in need of dextromethorphan treatment, wherein, on the eighth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for eight consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least eight consecutive days, to a human in need of dextromethorphan treatment, wherein, on the eighth day , the dextrorphan plasma level is lower than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without treohydroxybupropion or a prodrug thereof for eight consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising the co-administration of bupropion and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day, the plasma level of dextrorphan is less than the plasma dextrorphan level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, at / frZQnn / Lznz / E / Yii where, on the ninth day, the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without treohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of bupropion and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day, the plasma level of dextrorphan is less than the plasma dextrorphan level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without treohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of bupropion and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day, the plasma level of dextrorphan is less than the plasma dextrorphan level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for nine consecutive days / ^ζοηη / ίζηζ / Β / γι. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least nine consecutive days, to a human in need of dextromethorphan treatment, wherein, on the ninth day , the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without treohydroxybupropion or a prodrug thereof for nine consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of bupropion and dextromethorphan, for at least ten consecutive days, to a human in need of dextromethorphan treatment, wherein, on the tenth day, the plasma level of dextrorphan dextrorphan is less than the plasmatic level of dextrorphan that would have been obtained with the administration of the same amount of dextromethorphan administered without bupropion for ten consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least ten consecutive days, to a human in need of dextromethorphan treatment, wherein, on the tenth day , the plasmatic level of dextrorphan is less than the plasmatic level of dextrorphan that would have been obtained with the administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for ten consecutive days. Some modalities include a method of reducing plasma dextrorphan levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least ten consecutive days, to a human in need of dextromethorphan treatment, wherein, on the tenth day , the plasmatic level of dextrorphan is less than the plasmatic level of dextrorphan that would have been obtained with the administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for ten consecutive days. Some modalities include a method of reducing plasma dextrorphan levels which / ^ζοηη / ίζηζ / Β / γι comprises co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least ten consecutive days, to a human in need of treatment with dextromethorphan, wherein, on the tenth day, the dextrorphan plasma level is less than the dextrorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without threohydroxybupropion or a prodrug thereof for ten consecutive days. Antidepressant compounds, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to enhance the therapeutic properties, such as in the treatment of neurological disorders, of dextromethorphan. Bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, regardless of their stereochemistry, may be effective in inhibiting or reducing the metabolism of dextromethorphan in some humans. This can be accomplished by co-administering bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, and dextromethorphan. Some embodiments include a method of treating a neurological disorder comprising administering: 1) dextromethorphan or 2) a combination of an antidepressant compound and dextromethorphan to a human in need thereof, wherein the human is an extensive metabolizer of dextromethorphan. Some embodiments include a method of increasing dextromethorphan plasma levels in a human in need of dextromethorphan treatment, where the human is an extensive dextromethorphan metabolizer, comprising co-administering bupropion with dextromethorphan to the human. Some embodiments include a method of inhibiting the metabolism of dextromethorphan, comprising administering bupropion to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the human's body at the same time what bupropion. Some modalities include a method of increasing the metabolic life of dextromethorphan, comprising administering bupropion to a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan and where dextromethorphan is present in the body human at the same time as bupropion. Some modalities include a method of correcting extensive metabolism of dextromethorphan, comprising administering bupropion to a human in need thereof. Some embodiments include a method of enhancing the antitussive properties of dextromethorphan comprising administering bupropion in conjunction with administering dextromethorphan to a human in need of cough treatment. Some embodiments include a method of treating cough comprising administering a combination of bupropion or other active compound and dextromethorphan to a human in need thereof. Some modalities include a method of treating a neurological disorder comprising administering 1) dextromethorphan or 2) bupropion and dextromethorphan to a human in need thereof, / bzonn / i znz / E / Yl· wherein 1) dextromethorphan or 2) bupropion and dextromethorphan are given at least once daily for at least 8 days, at least 9 days, or at least 10 days. Some embodiments include a method of treating a neurological disorder comprising administering about 150 mg / day to about 300 mg / day of bupropion and about 15 mg / day to about 60 mg / day of dextromethorphan to a human in need thereof. Some modalities include a method of increasing dextromethorphan plasma levels in a human in need of dextromethorphan treatment, where the human is an extensive dextromethorphan metabolizer, comprising co-administering hydroxybupropion or a prodrug thereof with dextromethorphan to the human . Some modalities include a method of increasing dextromethorphan plasma levels in a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan, comprising co-administration of erythrohydroxybupropion or a prodrug thereof with dextromethorphan to the human . Some modalities include a method of increasing dextromethorphan plasma levels in a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan, comprising co-administration of threohydroxybupropion or a prodrug thereof with dextromethorphan to the human . Some embodiments include a method of inhibiting the metabolism of dextromethorphan, comprising administering bupropion to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the human's body at the same time what bupropion. Some embodiments include a method of inhibiting the metabolism of dextromethorphan, comprising administering hydroxybupropion or a prodrug thereof to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the body of the human. human at the same time as hydroxybupropion. Some embodiments include a method of inhibiting the metabolism of dextromethorphan, comprising administering erythrohydroxybupropion or a prodrug thereof to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the body of the human. human at the same time as erythrohydroxybupropion. Some embodiments include a method of inhibiting the metabolism of dextromethorphan, comprising administration of threohydroxybupropion or a prodrug thereof to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the body of the human. human at the same time as threohydroxybupropion. Some embodiments include a method of increasing the metabolic life of dextromethorphan, comprising administering hydroxybupropion or a drug thereof to a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan and where dextromethorphan it is present in the human body at the same time / frZQnn / Lznz / E / Yii as hydroxybupropion. Some embodiments include a method of increasing the metabolic life of dextromethorphan, comprising administering erythrohydroxybupropion or a drug thereof to a human in need of dextromethorphan treatment, where the human is an extensive metabolizer of dextromethorphan and where dextromethorphan it is present in the human body at the same time as erythrohydroxybupropion. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of bupropion and dextromethorphan to a human in need of dextromethorphan treatment, wherein bupropion is administered on the first day of at least two days of co-administration of bupropion with dextromethorphan , where an increase in the plasma level of dextromethorphan occurs on the first day that bupropion and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without bupropion. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the hydroxybupropion or prodrug thereof is administered on the first day of at least two days of co-administration of hydroxybupropion with dextromethorphan, where an increase in dextromethorphan plasma level occurs on the first day that hydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without hydroxybupropion or prodrug thereof. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the erythrohydroxybupropion or prodrug thereof is administered on the first day of at least two days of co-administration of erythrohydroxybupropion with dextromethorphan, where an increase in the plasma level of dextromethorphan occurs on the first day that erythrohydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without erythrohydroxybupropion or prodrug thereof. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need of dextromethorphan treatment, wherein the threohydroxybupropion or prodrug thereof is administered on the first day of at least two days of co-administration of threohydroxybupropion with dextromethorphan, where an increase in dextromethorphan plasma level occurs on the first day that threohydroxybupropion or a prodrug thereof and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without threohydroxybupropion or prodrug thereof. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of bupropion and dextromethorphan, for at least five / ^ζοηη / ίζηζ / Β / γι consecutive days, to a human in need of dextromethorphan treatment, wherein, on the fifth day, the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for five consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least five consecutive days, to a human in need of dextromethorphan treatment, wherein, on the fifth day , the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for five consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan, for at least five consecutive days, to a human in need of dextromethorphan treatment, wherein, on the fifth day , the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for five consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least five consecutive days, to a human in need of dextromethorphan treatment, wherein, on the fifth day , the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without threohydroxybupropion or a prodrug thereof for five consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of bupropion and dextromethorphan, for at least six consecutive days, to a human in need of dextromethorphan treatment, wherein, on the sixth day, the plasma level of dextromethorphan dextromethorphan is greater than the plasma dextromethorphan level that would have been obtained by administration of the same amount of dextromethorphan given without bupropion for six consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan, for at least six consecutive days, to a human in need of dextromethorphan treatment, wherein, on the sixth day , the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without hydroxybupropion or a prodrug thereof for six consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of erythrohydroxybupropion or a prodrug thereof / bZQnn / Lznz / E / Yi and dextromethorphan, for at least six consecutive days, to a human in need of dextromethorphan treatment , where, on the sixth day, the plasmatic level of dextromethorphan is higher than the plasmatic level of dextromethorphan that would have been obtained with the administration of the same amount of dextromethorphan administered without erythrohydroxybupropion or a prodrug thereof for six consecutive days. Some modalities include a method of increasing dextromethorphan plasma levels comprising co-administration of threohydroxybupropion or a prodrug thereof and dextromethorphan, for at least six consecutive days, to a human in need of dextromethorphan treatment, wherein, on the sixth day , the dextromethorphan plasma level is higher than the dextromethorphan plasma level that would have been obtained by administration of the same amount of dextromethorphan administered without threohydroxybupropion or a prodrug thereof for six consecutive days. Some modalities include a method of reducing a trough effect of dextromethorphan comprising co-administration of bupropion with dextromethorphan to a human patient in need of dextromethorphan treatment, wherein dextromethorphan has a plasma level 12 hours after bupropion co-administration with dextromethorphan that is at least twice the plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion. Some modalities include a method of reducing a "trough" effect of dextromethorphan comprising co-administration of hydroxybupropion or a prodrug thereof with dextromethorphan to a human patient in need of dextromethorphan treatment, wherein dextromethorphan has a plasma level 12 hours after co-administration of dextromethorphan. hydroxybupropion or a prodrug thereof with dextromethorphan that is at least twice the plasma level that would be obtained by administering the same amount of dextromethorphan without hydroxybupropion or a prodrug thereof. Some modalities include a method of reducing a "trough" effect of dextromethorphan comprising co-administration of erythrohydroxybupropion or a prodrug thereof with dextromethorphan to a human patient in need of dextromethorphan treatment, wherein dextromethorphan has a plasma level 12 hours after co-administration of dextromethorphan. erythrohydroxybupropion or a prodrug thereof with dextromethorphan that is at least twice the plasma level that would be obtained by administering the same amount of dextromethorphan without erythrohydroxybupropion or a prodrug thereof. Some modalities include a method of reducing a "trough" effect of dextromethorphan comprising co-administration of threohydroxybupropion or a prodrug thereof with dextromethorphan to a human patient in need of dextromethorphan treatment, wherein dextromethorphan has a plasma level 12 hours after co-administration of dextromethorphan. threohydroxybupropion or a prodrug thereof with dextromethorphan that is at least twice the plasma level that would be obtained by administering the same amount of dextromethorphan without threohydroxybupropion or a prodrug thereof. Some modalities include a method of reducing an adverse event associated with dextromethorphan treatment, comprising co-administration of bupropion and dextromethorphan to a human patient in need of dextromethorphan treatment, wherein the human patient is in / frZQnn / Lznz / E / Yii risk of experiencing the adverse event as a result of treatment with dextromethorphan. Some modalities include a method of reducing an adverse event associated with dextromethorphan treatment, comprising co-administration of hydroxybupropion or a prodrug thereof and dextromethorphan to a human patient in need of dextromethorphan treatment, where the human patient is at risk of experiencing the adverse event as a result of dextromethorphan treatment. Some modalities include a method of reducing an adverse event associated with dextromethorphan treatment, comprising co-administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan to a human patient in need of dextromethorphan treatment, where the human patient is at risk of experiencing the adverse event as a result of dextromethorphan treatment. Some modalities include a method of reducing an adverse event associated with bupropion treatment, comprising co-administration of dextromethorphan and bupropion to a human patient in need of bupropion treatment, where the human patient is at risk of experiencing the adverse event as a result. of bupropion treatment. Some modalities include a method of correcting extensive metabolism of dextromethorphan, comprising the administration of hydroxybupropion or a prodrug thereof, to a human in need thereof. Some modalities include a method of correcting extensive dextromethorphan metabolism, comprising administration of erythrohydroxybupropion or a prodrug thereof, to a human in need thereof. Some modalities include a method of correcting extensive dextromethorphan metabolism, comprising administration of threohydroxybupropion or a prodrug thereof, to a human in need thereof. Some embodiments include a method of enhancing the antitussive properties of dextromethorphan comprising administering bupropion in conjunction with administering dextromethorphan to a human in need of cough treatment. Some embodiments include a method of enhancing the antitussive properties of dextromethorphan comprising administration of hydroxybupropion or a prodrug thereof, in conjunction with administration of dextromethorphan to a human in need of cough treatment. Some embodiments include a method of enhancing the antitussive properties of dextromethorphan comprising administration of erythrohydroxybupropion or a prodrug thereof, in conjunction with administration of dextromethorphan to a human in need of cough treatment. Some embodiments include a method of enhancing the antitussive properties of dextromethorphan comprising administration of threohydroxybupropion or a prodrug thereof, in conjunction with administration of dextromethorphan to a human in need of cough treatment. Some modalities include a method of treating cough comprising the administration of / ΐτζοηη / ίζηζ / Β / γΐί a combination of hydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof. Some embodiments include a method of treating cough comprising administering a combination of erythrohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof. Some embodiments include a method of treating cough comprising administering a combination of threohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof. Some modalities include a method of treating a neurological disorder comprising the administration of bupropion and dextromethorphan to a human in need thereof, wherein bupropion and dextromethorphan are administered at least once daily for at least 8 days, at least 9 days, or at least 10 days. Some modalities include a method of treating a neurological disorder comprising the administration of hydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof, wherein the bupropion and dextromethorphan are administered at least once daily for at least 8 days , at least 9 days or at least 10 days. Some modalities include a method of treating a neurological disorder comprising the administration of erythrohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof, wherein the erythrohydroxybupropion and dextromethorphan are administered at least once daily for at least 8 days , at least 9 days or at least 10 days. Some modalities include a method of treating a neurological disorder comprising administration of threohydroxybupropion or a prodrug thereof and dextromethorphan to a human in need thereof, wherein threohydroxybupropion and dextromethorphan are administered at least once daily for at least 8 days, at least 9 days or at least 10 days. Some embodiments include a pharmaceutical composition, dosage form, or medicament comprising a therapeutically effective amount of dextromethorphan, a therapeutically effective amount of an antidepressant, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, and a pharmaceutically acceptable excipient. Some modalities include a method of reducing a risk of seizures associated with the use of bupropion to treat depression, comprising oral administration of a combination of dextromethorphan and bupropion twice daily, where the method is: 1) at least equal to effective in treating depression and 2) reduces the risk of seizures in humans, compared with oral administration of 150 mg bupropion alone twice daily to a human for the same number of days. Some modalities include a method of enhancing the therapeutic effect of bupropion to treat depression, comprising oral co-administration of dextromethorphan with a bupropion, twice daily, to a human suffering from depression, wherein the method is more effective than treating the / frZQnn / Lznz / E / Yii depression of said human with oral administration of bupropion 150 mg alone twice daily to human for five weeks. In some modalities, the combination of dextromethorphan and bupropion is more effective than single oral administration of the same amount of dextromethorphan or bupropion alone. Some modalities include a method of enhancing the efficacy of bupropion in the treatment of depression, comprising oral administration of about 90 mg to about 125 mg of bupropion in combination with about 0.3 mg / kg to about 1 mg / kg of dextromethorphan, once or twice daily for at least 23 days, to a human suffering from depression, wherein oral administration of bupropion in combination with dextromethorphan is more effective in treating depression than oral administration of the same bupropion dosage regimen without dextromethorphan. Some embodiments include a method of treating treatment-resistant depression comprising: selecting a human suffering from depression who has previously been unsuccessfully treated with at least one antidepressant; and oral administration of a combination treatment of dextromethorphan and bupropion once or twice daily to humans for at least about five weeks; wherein the combination treatment of dextromethorphan and bupropion comprises about 40 mg to about 70 mg of dextromethorphan and about 100 mg to about 140 mg of bupropion. Some modalities include a method of rapidly alleviating the symptoms of depression, comprising administering a combination of bupropion and dextromethorphan once or twice daily to a human in need thereof, wherein the human experiences a therapeutic effect within 2 weeks from the first day that the combination of bupropion and dextromethorphan was administered. Some modalities include a method of treating depression, comprising administering a combination of bupropion and dextromethorphan once or twice daily to a human in need thereof, where the human is of Asian descent. Some modalities include a method of treating nicotine addiction associated with tobacco smoking comprising administering a combination of a bupropion and a dextromethorphan for at least 21 consecutive days to a person suffering from nicotine addiction, wherein the person is an ad-lib tobacco user, where a total amount of 200 mg to 250 mg of bupropion and 80 mg to 140 mg of dextromethorphan is administered to the person daily, and where the method is more effective than self-administration amount of bupropion alone. In some modalities involving nicotine addiction, administration of the combination of bupropion and dextromethorphan results in at least a 20% greater reduction in intensity of nicotine self-administration compared to bupropion alone as measured by the reduction in the average number of cigarettes smoked per day. In some modalities involving nicotine addiction, administration of the combination of bupropion and dextromethorphan results in at least a 10% greater reduction in expelled carbon monoxide levels compared with bupropion alone. / frZQnn / Lznz / E / Yi In some modalities involving nicotine addiction, administration of the combination of bupropion and dextromethorphan twice daily in 2 equal divided doses results in a further reduction in the intensity of nicotine self-administration at a specific time point, as 1 week, 2 weeks, 3 weeks, 4 weeks, or other time point specified therein, than would have resulted from administration of one of the 2 divided doses for the same duration of time, or that would have resulted from do not administer the combination. Brief description of the figures Figure 1 is a graph of mean plasma dextromethorphan concentrations over time after dosing on Day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 2 shows the mean AUC0-12 of dextromethorphan on day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 3 shows the mean AUC0-24 of dextromethorphan on day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 4 shows the mean AUCo-inf of dextromethorphan on day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 5 shows the fold change in dextromethorphan AUC on day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 6 shows the mean AUC0-12 of dextromethorphan on day 1 and day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 7 shows the mean trough plasma concentrations of dextromethorphan for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 8 shows the mean peak plasma concentrations of dextromethorphan on day 1 and day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 9 is a graph of mean plasma dextrorphan concentrations over time after dosing on Day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 10 shows the mean peak plasma dextrorphan concentrations on day 1 and day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 11 shows the mean AUC0-12 of dextrorphan on day 1 and day 8 for subjects receiving dextromethorphan alone or dextromethorphan and bupropion. Figure 12 shows the potency of various antidepressant compounds with respect to inhibition of dextromethorphan metabolism in human liver microsomes. Figure 13 is a graph of the change from baseline in the mean MADRS total score over time during the 6-week dosing period for subjects receiving dextromethorphan alone or the combination of dextromethorphan and bupropion. Figure 14 shows the percentage of subjects achieving remission (MADRS < 10) over time during the 6-week dosing period for subjects receiving dextromethorphan alone or the combination of dextromethorphan and bupropion. Figure 15 is a graph of the reduction in MADRS total score over time for the subjects described in Example 6. Figure 16 is a graph of the percentage of patients who responded to treatment over time for the subjects described in Example 6. Figure 17 is a graph of the percentage of subjects in remission over time for the subjects described in Example 6. Detailed description of the invention Some modalities include a method of treating neurological disorders comprising administration of a therapeutically effective amount of dextromethorphan and a therapeutically effective amount of an antidepressant, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, at a person who needs it. Some modalities include a method of enhancing the therapeutic properties of dextromethorphan for treating neurological disorders, comprising co-administration of dextromethorphan and an antidepressant, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. Some embodiments include a method of increasing plasma dextromethorphan levels in a human who is an extensive dextromethorphan metabolizer, comprising co-administration of an antidepressant compound, such as bupropion, and dextromethorphan to the human. Some modalities include a method of inhibiting the metabolism of dextromethorphan, comprising administering an antidepressant compound, such as bupropion, to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the body of the human at the same time as the antidepressant. Some modalities include a method of increasing the metabolic life of dextromethorphan, including an increase in the elimination half-life (T1 / 2) of dextromethorphan. These modalities may comprise administration of an antidepressant compound, such as bupropion, to a human, where the human is an extensive metabolizer of dextromethorphan, and where dextromethorphan is present in the human's body at the same time as the antidepressant compound. . Some modalities include a method of correcting extensive dextromethorphan metabolism, comprising administering an antidepressant compound, such as bupropion, to a human in need thereof, such as a human in need of pain treatment. Some embodiments include a method of enhancing the therapeutic properties of dextromethorphan to treat neurological treatments comprising administering an antidepressant compound, such as bupropion, in conjunction with administering dextromethorphan to a human in need of treatment for a neurological disorder. Some modalities include a method of treating neurological disorders comprising administering a combination of an antidepressant compound, such as bupropion, and dextromethorphan to a human in need thereof. Co-administration of an antidepressant compound, such as bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a prodrug of the antidepressant compound, with dextromethorphan, may occur one or more times in a single day, or for 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100 or more consecutive days. In some modalities, co-administration is at least once a day for at least two consecutive days. In some modalities, co-administration of an antidepressant compound, such as bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a prodrug of the antidepressant compound, with dextromethorphan, can occur once daily for 1, 2, 3, 4, 5, 6, or 7 days. , prior to co-administration twice daily. Dextromethorphan has the structure shown below. / ^ζοηη / ίζηζ / Β / γι Dextromethorphan is used as a cough suppressant. According to the FDA's dextromethorphan product labeling requirement under the Over-the-Counter (OTO) product monograph [21CFR341.74], dextromethorphan should be dosed 6 times daily (every 4 hours), 4 times daily (every 6 hours) or 3 times a day (every 8 hours). The OTC monograph [21CFR341.74] also states that “dosage is equivalent to dextromethorphan hydrobromide...oral dosage is 10 to 20 milligrams every 4 hours or 30 milligrams every 6 to 8 hours, not to exceed 120 milligrams in 24 hours, or as directed by the doctor. Dextromethorphan is rapidly metabolized in the human liver. This rapid hepatic metabolism may limit systemic drug exposure in people who are extensive metabolizers. Humans can be: 1) extensive metabolizers of dextromethorphan, those who metabolize dextromethorphan rapidly; 2) poor dextromethorphan metabolizers, those who only have poor dextromethorphan metabolism; or 3) intermediate dextromethorphan metabolizers, those with dextromethorphan metabolism somewhere between an extensive metabolizer and a poor metabolizer. Extensive metabolizers can also be ultra-rapid metabolizers. Extensive dextromethorphan metabolizers are a significant portion of the human population. Dextromethorphan can be metabolized, for example, to dextrorphan. When the same oral dose of dextromethorphan is administered, plasma dextromethorphan levels are significantly higher in poor or intermediate metabolizers compared to extensive dextromethorphan metabolizers. The low plasma concentrations of dextromethorphan may limit its clinical utility as a single agent for extensive metabolizers, and possibly intermediate metabolizers, of dextromethorphan. Some therapeutically active compounds, including antidepressants such as bupropion, inhibit the metabolism of dextromethorphan and increase the plasma concentration of dextromethorphan and therefore may improve its therapeutic efficacy. Similarly, antidepressants may allow dextromethorphan to be given less frequently, such as once a day instead of twice a day, once a day instead of three times a day, once a day instead of four times a day, twice a day instead of three times a day or twice a day instead of four times a day, without loss of therapeutic efficacy. Co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan, may improve the mechanisms of action or pharmacological properties of dextromethorphan and dextrorphan. Mechanisms of action of dextromethorphan and dextrorphan may include sigma-1 agonist and NMDA antagonist properties, calcium channel blockade, muscarinic binding, serotonin transporter (5HTT) inhibition, and mu receptor potentiation. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to agonize, antagonize, or modulate a sigma-1 receptor or an NMDA receptor, to block a calcium channel, to bind to a muscarinic receptor, to inhibit a serotonin transporter (5HTT), or to potentiate a mu receptor. The pharmacological properties of dextromethorphan and dextrorphan may include antagonism of the NMDA high affinity site, of NMDR-2A and of the functional NMDR-2B receptor, stimulation of sigma-1, activation of putative mTOR (by sigma-1 stimulation). 1, mu potentiation, beta adrenergic receptor stimulation, and 5HTT inhibition), putative AMPA receptor trafficking (via mTOR activation, PCP antagonism, sigma-1 stimulation, beta stimulation, mu potentiation, and 5HTT inhibition), and dendritogenesis, spinogenesis, synaptogenesis, and neuronal survival via NMDA antagonism and sigma-1 and mTOR signaling. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to bind, agonize, antagonize, stimulate, activate, inhibit, influence trafficking of, or modulate a high-affinity site of NMDA, NMDR-2A, a functional NMDR-2B receptor, a sigma-1 receptor, a putative mTOR receptor (such as by sigma-1 stimulation, potentiation of a mu receptor, stimulation of a beta adrenergic receptor or inhibition of a 5HTT) or a putative AMPA receptor (such as by activation of mTOR, antagonism of PCP activity, stimulation of a / bzonn / i znz / E / Yl receptor sigma-1, stimulation of a receptor beta adrenergic receptor, potentiation of a mu receptor, or inhibition of 5HTT). Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to cause, increase, reduce, or otherwise modulate dendritogenesis, spinogenesis, or synaptogenesis. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to cause, increase, reduce, or otherwise modulate neuronal survival through NMDA antagonism and / or sigma-1 signaling and / or mTOR. The pharmacological properties of dextromethorphan and dextrorphan may include 5HTT and norepinephrine transporter inhibition, sigma-1 stimulation, NMDA and PCP antagonism, and possible serotonin 5HT1b / d receptor stimulation. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to bind, agonize, antagonize, stimulate, activate, inhibit, influence trafficking of, or modulate the 5HTT and / or norepinephrine transporter, the sigma-1 receptor, the NMDA and / or PCP receptor and / or to stimulate the 5HT1b / d serotonin receptor. Additional properties of dextromethorphan and dextrorphan may include possible presynaptic alpha-2 adrenergic receptor antagonism or postsynaptic alpha-2 stimulation, beta stimulation, and possible muscarinic and mu receptor antagonism. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to bind, agonize, antagonize, stimulate, activate, inhibit, influence trafficking of, or modulate a presynaptic alpha-2 adrenergic receptor, postsynaptic alpha-2 receptor, beta adrenergic receptor, muscarinic receptor, or mu receptor. Dextromethorphan and dextrorphan may be glial cell modulators. Some modalities include co-administration of an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan or dextrorphan to modulate glial cells. Pain or other neurological disorders can be treated by improving plasma dextromethorphan levels or increasing the bioavailability of dextromethorphan, for example, by a method comprising administration of a therapeutically effective amount of dextromethorphan and a therapeutically effective amount of an antidepressant compound, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, to a person in need thereof. Examples of neurological disorders that can be treated, or can be treated with enhanced efficacy, by enhanced levels of dextromethorphan, such as those that can be achieved by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these / nzonn / i zoz / e / yl compounds, include, without limitation: affective disorders, psychiatric disorders, brain function disorders, movement disorders, dementias, motor neuron diseases, neurodegenerative diseases, seizure disorders, and headache. Mood disorders that can be treated by enhanced levels of dextromethorphan or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, without limitation, depression, major depression, treatment-resistant depression and treatment-resistant bipolar depression, bipolar disorders including cyclothymia, seasonal affective disorder, mood disorders, chronic depression (dysthymia), psychotic depression, postpartum depression, premenstrual dysphoric disorder (PMDD) , situational depression, atypical depression, mania, anxiety disorders, attention deficit disorder (ADD), attention deficit hyperactivity disorder (ADHD) and attention deficit / hyperactivity disorder (ADHD), bipolar and manic condition , obsessive-compulsive disorder, bulimia, obesity or weight gain, narcolepsy, chronic fatigue syndrome, premenstrual syndrome, substance abuse or addiction, nicotine addiction, psychosexual dysfunction, affective incontinence, and emotional instability. Depression can manifest itself through symptoms of depression. These symptoms may include psychological changes such as mood swings, feeling intensely sad, hopeless, mental slowness, loss of concentration, pessimistic worry, agitation, anxiety, irritability, guilt, anger, feelings of worthlessness, irresponsible behavior, thoughts suicide or suicide attempts and / or self-contempt. Physical symptoms of depression may include insomnia, anorexia, loss of appetite, weight loss, weight gain, loss of energy and libido, fatigue, restlessness, pain, headache, cramps, digestive problems, and / or abnormal hormonal circadian rhythm. Some patients may have inadequate or no response to treatment even after treatment with medications such as antidepressants. Treatment-resistant depression (TRD), or treatment-refractory depression, is a condition usually associated with patients who have been unsuccessful with at least two antidepressants. Part of the diagnosis of TRD is that the patient has had an inadequate response to treatment with antidepressants after an adequate dose and adequate course. TRD may be more difficult to treat due to comorbidity with other medical or psychological conditions, such as drug / alcohol abuse or eating disorders, or a misdiagnosis of TRD. Some patients with TRD have had an inadequate response to 1,2, 3 or more trials of adequate antidepressant treatment or had no response or had an inadequate response to 1,2, 3 or more prior antidepressant treatments. In some modalities, a patient being treated for treatment-resistant depression has been unsuccessful with treatment with at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more antidepressant therapies. Measures of treatment effect that can be enhanced by treatment with improved bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant, such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these composites, include, without limitation: Rating Scale 7b7Qnn / l 7n7 / E / Yl · The Montgomery-Asberg Depression Questionnaire (MADRS), the Short-Form Life Quality and Satisfaction Questionnaire, the Interval of Impairment in Functioning Tool, the Scale of Sheehan's Disability, Patient-Rated Inventory of Side Effects (FRISE), Columbia Suicide Severity Rating Scale (CSSRS), Suicide Rapid Inventory Depression, Self Report (QIDS-SR), Clinical Global Impression (CGI) scale, Massachusetts General Hospital Cognitive and Physical Functioning Questionnaire (CPFQ) the 17-item Hamilton Depression Rating Scale (HAM-D17), the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire (MGH ATRQ), the Rapid Inventory of 16-Item Depression Symptomology - Self-Report (QIDS-SR16), Sheehan Disability Scale (SDS), Clinical Global Impression of Illness Severity (CGI) -S), Clinical Global Impression of Change (CGI-C), EuroQOL 5 Dimensions 5 Levels (EQ-5D-5L), Patient Global Impression of Change (PGIC ), 7-item Generalized Anxiety Disorder (GAD-7), Clinical Global Impressions - Improvement (CGI-I). Sheehan Disability Scale (SDS). 16-item Rapid Inventory of Depression Symptomology - Self-Report (QIDS-SR16), Hamilton Anxiety Scale (HAM-A), Massachusetts General Hospital Questionnaire of Cognitive and Physical Functioning (CPFQ), CPFQ-Cognitive subscales (items 4 to 7), Brief Psychiatric Rating Scale (BPRS), etc.; the Digit Symbol Substitution Test (DSST), the Rey Auditory Verbal Learning Task (RAVLT), the Tracing Test (TMT), Stroop Colors and Words Test (STROOP), Simple Reaction Time (SRT), Choice Reaction Time (CRT), etc. In some modalities, treating a person with a combination of dextromethorphan and bupropion can improve (eg, lower) the person's score on one of the above assessments by at least about 10%, at least about 20%, by at least about 30%, at least about 40%, at least about 50%, about 10-20%, about 20-30%, about 30-40%, about 40-50%, about 5-15%, about 15-25% , about 25-35%, about 35-45%, about 45-55%, about 50-60%, about 60-70%, about 70-80%, about 80-90%, about 90-100% compared to the reference or placebo. In some modalities, improvement is compared to baseline. In some modalities, improvement is compared to placebo. Administration of a combination of bupropion and dextromethorphan may result in rapid treatment effect, e.g., within approximately 1 week, within approximately 2 weeks, within approximately 3 weeks, or within approximately 4 weeks from the start of treatment. treatment. For example, an improvement in any of the assessments described herein, including, without limitation, MADRS, the Quality and Satisfaction of Life Questionnaire Short Form, the Interval of Impairment in Functioning Tool, FRISE, C-SSRS, QIDS -SR), CGI, CPFQ, HAMD17, MGH ATRQ, CGI-S, CGI-C, EQ-5D-5L, PGIC, GAD-7, CGI-I, SDS, QIDS-SR16, HAM-A, CPFQ, subscales of CPFQ-Cognitive (points 4 to 7), BPRS, DSST,RAVLT, TMT, STROOP, SRT, CRT, etc., can be observed within said time points. In some modalities, an enhanced bioavailability of dextromethorphan or a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, may have an onset of action within 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 6-8 hours, 8-12 hours, 12 hours, one day, 1-7 days, 1 week, two weeks, three weeks, four weeks, six weeks or eight weeks. Patients who may benefit from the treatments described herein include pediatric patients, such as patients less than approximately 18 years of age, approximately 0-5 years of age, approximately 5-10 years of age, approximately 10-12 years of age, or approximately 12-18 years of age; adult patients, such as patients of an age of about 18-70 years, about 18-65 years, about 18-30 years, about 30-50 years, about 50-65 years; and elderly patients, such as patients over 65 years of age, about 65-75 years of age, about 75-90 years of age, or over 90 years of age. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being of Asian descent. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being of Japanese descent. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being of Korean descent. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being of Chinese descent. Assignment of a person as being of Asian, Chinese, Japanese, or Korean descent may be based on that person's self-report. In these Asian people, the combination of dextromethorphan and bupropion may be effective in treating depression, where bupropion alone is not. This may be particularly important because patients of Asian descent may have more severe depression than those of other ethnic or cultural groups. In some modalities, the human does not have or is selected for not having a depressive episode with psychotic or catatonic features. In some modalities, the human does not have or is selected not to have a manic, hypomanic, or mixed episode, including bipolar disorder (type 1 or type 2) and a substance-induced (eg, antidepressant-induced) manic episode. ) or a hypomanic / mixed episode. In some embodiments, the human does not have or is selected for not having schizophrenia, / bzonn / i znz / E / Yl· schizoaffective disorder, or another psychotic disorder. In some modalities, the human does not have or is selected for not having a panic disorder, with or without agoraphobia. In some modalities, the human being does not have or is selected for not having obsessive-compulsive disorder. In some modalities, the human being does not have or is selected for not having bulimia or anorexia nervosa. In some modalities, the human does not have or is selected for not having a persistent neurocognitive disorder. In some modalities, the human does not have or is selected for not having any anxiety disorder during the six months prior to treatment. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a diagnosis of major depressive disorder according to the Diagnostic and Statistical Manual of Mental Disorders (Diagnostic and Statistical Manual of Mental Disorders), Fourth Edition, Textual Review (DSM-IV-TR), the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders. ), Fifth Edition, Clinical Trials Version SCID-5-CT. In some modalities, the human currently meets the DSM-5 criteria for MDD without psychotic features, based on SCID-5-CT In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a major depressive episode that has lasted approximately 1-2 years, at least about 1 week, at least about 2 weeks, at least about 3 weeks, at least about 4 weeks, at least about 6 weeks, at least about 2 months, at least about 3 months, at least about 4 months, at least about 6 months, at least approximately 9 months, at least approximately 1 year, at least approximately 18 months, at least approximately 2 years, approximately 1 -12 weeks, approximately 3-6 months, approximately 6-9 months, approximately 9-12 months , about 12-18 months, about 18-24 months, about 2-4 years, about 4-6 years, about 6-10 years, about 10-20 years or more. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having approximately 1-100 or more depressive episodes in their lifetime, such as major depressive episodes, including at least 1, at least about 2, at least about 3, at least about 4, at least about 5, at least about 10, at least about 15, at least about 20, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 80, at least about 90, at least about 100, about 1-5, about 5-10, about 10-20, about 20-30, about 30-40, about 40-50, about 50-60, about 60-70, about 70-80, about 80-90, about 90-100 or approximately 4-7 depressive episodes during their lifetime. / frZQnn / Lznz / E / Yii In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having an inadequate response to one or more prior antidepressant therapies, eg, 1,2, 3, 4, 5 or more prior antidepressant therapy, including prior antidepressant therapy in the current depressive episode (eg, current major depressive episode). In some modalities, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression had or is selected for having had background antidepressant therapy with, for example, a selective inhibitor of the reuptake of serotonin inhibitor (SSRI), a serotonin norepinephrine reuptake inhibitor (SNRI), or bupropion, taken at an adequate dose for at least 8 weeks and at a stable dose for at least 4 weeks weeks before entering modalities, antidepressant therapy continues bupropion and dextromethorphan. In some modalities, the human to the double-blind treatment period. In some in conjunction with treatment with the combination of treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being male. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression is or is selected for being female. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has or is selected to have a body mass index of about 18-40 kg / m2, about 18-22 kg / m2, approximately 22-24 kg / m2, approximately 24-26 kg / m2, approximately 30-32 kg / m2, approximately 36-38 kg / m2, approximately 26-28 kg / m2, approximately 32-34 kg / m2, approximately 38-40 kg / m2, approximately 28-30 kg / m2 approximately 34-36 kg / m2 approximately 18-26 kg / m2 approximately 26-34 kg / m2 or approximately 34-40 kg / m2. The MADRS is a clinical rating scale. The MADRS is used to assess the symptomatology of depression during the previous week. Subjects are scored on 10 items to assess feelings of sadness, lassitude, pessimism, internal tension, suicidal thinking, reduced sleepiness or appetite, difficulty concentrating, and lack of interest. Each item is rated on a 7-point scale. A score of 0 indicates no symptoms and a score of 6 indicates symptoms of maximum severity. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has or is selected for having a MADRS score that is at least about 25, at least about 30, of at least about 35, at least about 40, at least about 45, at least about 50, at least about 55, about 20-25, about 25-30, about 30-35, about 35 -40, about 40-45, about 45-50, about 50-55, about 55-60, about 25-35, about 35-45, about 45-60, about 25-40 , or about 40-60. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a MADRS score reduced by at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, about 10-20%, about 20-30%, about 30-40%, about 40-50%, about 50-60%, about 60-80%, about 80-90% or about 90 -100% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, treatment with the combination of dextromethorphan or bupropion results in the human having a MADRS score that is less than 34, approximately 20-34, approximately 7-19, approximately 0-6, approximately 30 or younger, about 26 or younger, about 25 or younger, about 20 or younger, about 17 or younger, about 14 or younger, about 12 or younger, about 10 or younger, about 8 or younger , about 6 or less, about 5 or less, about 4 or less, about 3 or less, about 2 or less, about 1 or less, about 0, about 0.1-6, about 0.1 -1, about 1-2, about 2-3, about 3-4, about 4-5, about 5-6, about 6-7, about 7-8, about 8-9 , about 9-10, about ΙΟ11, about 11-12, about 12-13, about 13-14, about 14-15, about 15-16, about 16-17, about 17 -18, about 18-19, about 19-20, about 18-20, about 0.1-3, about 3-6, about 6-9, about 9-12, about 12-14 , about 12-15, or about 15-20. The MADRS-6 subscale is the sum of responses to six of the 10 MADRS items believed to represent the core symptoms of depression: reported sadness, apparent sadness, internal tension, lassitude, inability to feel, and pessimistic thinking. MADRS items not included in the MADRS-6 score are reduced sleep, reduced appetite, difficulty concentrating, and suicidal thoughts. A higher MADRS score indicates more severe depression and each item provides a score from 0 to 6. The overall score ranges from 0 to 60. The questionnaire includes questions on the following symptoms 1. Apparent sadness 2. Reported sadness 3. Internal tension 4. Reduced sleep 5. Reduced appetite 6. Concentration problems 7. Lassitude 8. Inability to feel 9. Pessimistic thoughts 10. Suicidal thoughts. The usual cut-off points / ^ζοηη / ίζηζ / Β / γι are: a) 0 to 6 - normal / absence of symptoms; b) 7 to 19 - mild depression; c) 20 to 34 - moderate depression; and d) >34 severe depression. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has, or is selected to have, a MADRS6 score that is at least about 15, at least about 18, at least about 20, at least about 21, at least about 24, at least about 27, at least about 30, at least about 33, about 15-18, about 18-21, about 21-24 , about 24-27, about 27-30, about 30-33, about 30-34, about 33-36, at least about 34, about 7-19, about 15-19, about 1524, about24-30, about 20-34, or approximately 30-36, before starting treatment. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a MADRS-6 score reduced by at least about 10%, at least about 20%, at least about 30%, at least about 40 % or at least about 50%, about 10-20%, about 20-30%, about 30-40%, about 40-50%, about 50-60%, about 60-80%, about 80-90% or about 90 -100% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a MADRS-6 score that is approximately 17 or less, approximately 15 or less, approximately 10 or less, approximately 8 or less, approximately 6 or less, about 5 or less, about 4 or less, about 3 or less, about 2 or less, about 1 or less, about 0.1-6, about 0.1-1, about 1-2, about 2-3, about 3 -4, about 4-5, about 5-6, about 6-7, about 7-8, about 8-9, about 9-12, about 12-15, about 0.1-3, about 3-6, about 6 -8, about 6-9 or about 9-15. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a MADRS item 1 (apparent sadness) score that is 2, 4 or 6 before starting treatment. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a MADRS item 1 score reduction that is at least about 10%, at least about 20%, at least about 30 %, at least about 40%, or at least about 50% compared to control or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, / frZQnn / Lznz / E / Yi reduction is compared to placebo. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a MADRS item 1 score that is approximately 2 or less. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the beginning or end of the 16 week or at any other time. In some modalities, the treatment effect is assessed weekly using MADRS. The CGI-S scale is a clinical rating scale used to rate the severity of a subject's current state of mental illness compared to a population of MDD subjects. The subject is rated on a scale of 1 to 7, where 1 indicates a "normal state" and 7 indicates "among the most extreme disease subjects." The CGI-S can be administered by a person with extensive professional training and experience in evaluating mental illness. The possible scores are: 1) Normal, without any disease; 2) Borderline mental illness; 3) Mild illness; 4) Moderate disease; 5) Marked disease; 6) Serious illness; and 7) Among patients with more extreme disease. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a Clinical Global Impression-Severity (CGI-S) score that is at least least about 3, at least about 4, at least about 5, at least about 6, about 7, about 3-7, about 4-7, about 3-4, about 4-5, about 5-6, or about 6- 7. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in the CGI-S score that is at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in CGI-S score that is at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, about 0.1-6, about 0.1-1, about 1-2, about 2-3, about 3-4, about 4-5, about 5-6, about 0.1-3 or about 3-6. In some embodiments, the / ^ζοηη / ίζηζ / Β / γι reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-6, weeks 2-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. The 16-item QIDS-SR-16, a rating scale per patient, is an abbreviated version of the 30-item Inventory of Depression Symptomology (IDS) and is designed to assess the severity of depressive symptoms. QIDS-SR-16 assesses symptom criteria domains to diagnose a major depressive episode. QIDS-SR can be used to assess the subject's depression symptomatology during the previous 7 days. Subjects report symptom severity with respect to 10 items: sleep, feelings of sadness, appetite, weight changes, concentration, self-esteem, suicidal thinking, general interest level, energy level, psychomotor retardation, and restlessness. Each item can be rated on a 4-point scale where a score of 0 reflects no symptoms and a score of 3 reflects most severe symptoms. Total QIDS scores range from 0 to 27, where scores of 5 or less indicate no depression, scores of 6 to 10 indicate mild depression, 11 to 15 indicate moderate depression, 16 to 20 indicate severe depression, and total scores higher than 21 indicate very severe depression. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has, or is selected to have, a QIDSSR-16 score that is at least about 16, at least about 18, at least about 21, at least about 24, at least about 27, at least about 30, at least about 33, about 16-18, about 16-19, about 16-20, about 18-21, about 21-24, approximately 24-27, approximately 15-21 or approximately 21-27 before starting treatment. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in QIDS-SR-16 score that is at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% compared to control or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a QIDS-SR-16 score that is approximately 6 or less, / frZQnn / Lznz / E / Yii approximately 5 or less, approximately 4 or less less, about 3 or less, about 2 or less, about 1 or less, about 0.1-6, about 0.1-5, about 0.1-1, about 1-2, about 2-3, about 3-4, about 4- 5, about 5-6, about 0.1-3, or about 3-6. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or at the end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or at the end of week 15, at the start or end of week 16, or at any other time. The CGI-I scale is a clinical rating scale used to rate overall improvement or worsening of mental illness regardless of whether or not it is considered by the investigator to be an outcome of drug treatment. The subject is rated on a scale of 1 to 7, where 1 indicates that the subject has improved too much and 7 indicates that the subject has gotten too bad. The CGI-I can be administered by a person with extensive professional training and experience in evaluating mental illness. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a CGI-I score that is approximately 3 or less, approximately 2 or less, approximately 1, approximately 1-2, or approximately 2-3. . The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. The VAMS is a patient-rated mood scale consisting of a 100-mm line with a sad face at one end and a happy face at the other. Each end of the line can be additionally anchored by a word that describes the extremes of the mood. Subjects are to rate their mood by placing a mark on the line. Distance on the line is measured and calculated as a numerical score from 0 to 100. Subjects may be asked to complete the VAMS daily. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has or is selected for having a VAMS score that is at least about 40 mm, at least about 50 mm, at less / ^ζοηη / ίζηζ / Β / γι about 60 mm, at least about 70 mm, at least about 80 mm, at least about 90 mm, about 40-50 mm, about 50-60 mm, about 60-70 mm, about 70-80mm, about 80-90mm, about 90-100mm, about 40-60mm, about 60-80mm or about 80-100mm. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in the VAMS score that is at least about 10%, at least about 20%, at least about 30%, at least about 40 % or at least approximately 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, treatment with the combination of dextromethorphan and bupropion results in the human having a VAMS score that is less than approximately 50 mm, less than approximately 40 mm, less than approximately 30 mm, less than approximately 20 mm, less about 10mm, about 0-10mm, about 10-20mm, about 20-30mm, about 30-40mm, about 40-50mm, about 0-25mm or about 25-50mm. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. The Columbia Suicide Severity Rating Scale (C-SSRS) is a clinical scoring instrument that reports the severity of suicidal ideation and behavior. Suicidal ideation is rated on a 5-point scale: 1 (want to die), 2 (non-specific active suicidal thoughts), 3 (active suicidal ideation by any method [no plan] with no intention to act), 4 (suicidal ideation active with some intention to act, without a specific plan) and 5 (active suicidal ideation with a specific plan and intention). The C-SSRS also captures information about the intensity of ideation, specifically the frequency, duration, controllability, deterrents, and motives behind the most severe types of ideation. Suicidal behavior is rated on a 5-point scale: 0 (no suicidal behavior), 1 (preparatory actions or behavior), 2 (aborted attempt), 3 (disrupted attempt), and 4 (actual attempt). More than 1 rating can be selected as long as they represent multiple episodes. For actual attempts only, actual or potential lethality is ranked for initial, most lethal, and most recent attempts. The C-SSRS can be administered whenever a person undergoing treatment consults a / ^ζοηη / ίζηζ / Β / γι health professional. The C-SSRS can be completed for the subject's lifetime history of suicidal ideation and behavior, along with a period of recent recall. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in Columbia Suicide Severity Rating Scale (C-SSRS) score that is at least approximately 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% compared to control or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The effect of treatment can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. The Sheehan Disability Scale (SDS) is a personal rating instrument used to measure the effect of a patient's symptoms on the following three aspects: work / study, social life, and family / home responsibilities. For each of the three items, the scores range from 0 to 10. The number most representative of the degree of disruption in each area due to symptoms is marked on the line from 0 (not at all) to 10 (extremely). The three items or domains can be summarized to assess overall functional impairment by aggregating scores from each of the three items or domains, resulting in overall SDS score ranges of 0 (no impairment) to 30 (major impairment). . In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a Sheehan Disability Scale (SDS) score that is: for each SDS item (0-10 scale) at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9; and for the total SDS score at least about 5, at least 10, at least about 20, about 10-15, about 15-20, about 20-25, or about 25-30. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in SDS score that is at least about 10%, at least about 20%, at least about 30%, at least about 40 % or at least approximately 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. Treatment effect can be assessed at any appropriate time, such as during / ^ζοηη / ίζηζ / Β / γι weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at start or end of week 4, start or end of week 5, start or end of week 6, start or end of week 7, start or end of week 8, at beginning or end of week 9, beginning or end of week 10, beginning or end of week 11, beginning or end of week 12, beginning or end of week 13, at beginning or end of week 14, beginning or end of week 15, beginning or end of week 16, or any other time. The Hamilton Depression Rating Scale (HAM-D, HRSD, HDRS, or HAM-D17) is a 17-point clinical rating scale used to rate a subject's depressive state based on feelings of depression, guilt, thought suicidal, anxiety, agitation, level of understanding, insomnia patterns, loss of interest in work and other activities, weight loss, hypochondriasis, and degree of psychomotor retardation. It can also be used to identify genital and somatic symptoms. Articles are rated on a scale of 0-2 or 0-4. A higher score indicates greater severity. For example, a depression level HAM-D score of 10-13 is considered mild; 14-17 is considered mild to moderate; and >17 is considered moderate to severe. In some embodiments, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has, or is selected to have, a HAMD score that is at least about 16, at least about 19 , at least about 21, at least about 24, at least about 27, at least about 30, at least about 33, at least about 36, about 16-19, about 18-21, about about 21-24, about 24-27, about 27-30, about 30-33, about 33-36, about 36-40, about 15-24, about 24-33, or about 33-40, or over 40 before starting treatment. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in HAM-D score that is at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. In some modalities, / ^ζοηη / ίζηζ / Β / γι the treatment effect is assessed weekly using HAM-D. Conversion of MADRS scores to HAM-D scores and vice versa can be accomplished using the following table. / frZQnn / Lznz / E / Yii Total Scores Score Change Percentage for Score Change MADRS HAMD MADRS HAMD MADRS HAMD - 100 -98 -96 -97 -94 -92 3 3 -37 -27 -94 - 90 4 4 -36 -26 -92 - 88 5 4 -35 -25 -90 - 86 6 5 -34 -25 -88 - 84 7 6 -33 -24 -86 - 83 8 7 -32 -23 -84 - 81 9 7 -31 -23 -82 - 80 10 8 -30 -22 -80 - 79 11 9 -29 -22 -78 - 77 12 9 -28 -21 -76 - 75 13 10 - 27 -20 -74 - 74 14 11 -26 -20 -72 - 73 15 12 -25 - 19 -70 - 72 16 12 - 24 - 18 -68 - 70 17 13 -23 - 18 -66 - 67 18 14 - 22 - 17 -64 - 65 19 15 - 21 - 16 -62 - 62 20 16 - 20 - 16 -60 - 61 21 16 - 19 - 15 -58 - 59 22 17 - 18 - 14 -56 - 57 23 18 - 17 - 14 -54 - 56 24 19 - 16 - 13 -52 - 54 25 19 - 15 - 12 -50 - 52 26 20 - 14 - 12 -48 - 50 27 21 - 13 - 11 -46 -48 28 22 - 12 - 10 -44 -47 29 23 - 11 - 9 -42 -45 30 23 - 10 - 9 -40 -43 31 24 -9 - 8 -38 -41 32 25 -8 - 7 -36 -39 33 25 - 7 - 6 -34 -37 34 26 -6 - 6 -32 -35 35 27 -5 - 5 -30 -33 36 28 -4 - 4 -28 -31 37 29 -3 -3 -26 -29 38 29 - 2 -2 -24 - 27 39 30 - 1 - 1 -22 -25 40 31 0 - 1 -20 -23 41 32 1 0 -18 -21 42 33 2 1 -16 - 19 43 34 3 2 -14 - 17 44 35 4 2 -12 - 15 45 35 5 3 -10 - 13 46 36 6 4 - 8 - 11 Total Scores Score Change Percentage for Score Change MADRS HAMD MADRS HAMD MADRS HAMD 47 37 7 4 - 6 - 9 48 37 8 5 - 4 - 7 49 38 - 2 - 5 50 38 0 -3 51 39 2 0 52 40 4 1 53 40 6 2 8 4 10 5 12 7 14 9 16 10 18 11 20 13 22 15 24 17 26 18 28 19 30 20 32 21 34 22 36 24 38 26 40 28 A negative value means an improvement. / frZQnn / Lznz / E / Yii The Hamilton Anxiety Scale (HAM-A) is a technician-applied scale consisting of 14 items, each rated on a five-point scale ranging from 0 (not present) to 4 (very severe). The highest possible total score is 56, which represents the most severe form of anxiety; the lowest possible score is 0, which represents no anxiety. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a score on the Hamilton Anxiety Scale (HAM-A) that is at least least about 20, at least about 25, at least about 30, at least about 35, at least about 40, at least about 45, at least about 50, at least about 55, about 20-25, about 25-30, about 30-35, about 35-40, about 4045, about 45-50, about 50-56, about 25-35, about 35-45, about 45-56, about 25-40 or about 40-56. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in HAM-A score that is at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least about 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. The Massachusetts General Hospital Cognitive and Physical Functioning Questionnaire (CPFQ) is a 7-item, patient-rated scale used to measure cognitive and executive dysfunction in mood and anxiety disorders that was developed to assess clinically relevant cognitive and physical symptoms that may arise or persist during long-term treatment for depression. Subjects rate the perceived quality of their physical and cognitive functioning. The score is 1-6 with increasing severity that individually assesses 7 different items: motivation / enthusiasm, alertness / alertness, energy, concentration / attention, recall ability, word finding ability, and alertness / mental acuity. The physical dimension of the CPFG assesses sleepiness and fatigue, and the cognitive dimension assesses apathy, inattention, memory loss, word-finding difficulties, and mental slowness. A higher score indicates greater impairment. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in CPFG score that is at least about 10%, at least about 20%, at least about 30%, at least about 40 % or at least approximately 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in the CPFG-Cognitive subscale score (items 4-7) that is at least approximately 10%, at least approximately 20 %, at least about 30%, at least about 40%, or at least about 50% compared to control or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of / ^ζοηη / ίζηζ / Β / γι week 12, at the start or end of week 13, at beginning or end of week 14, beginning or end of week 15, beginning or end of week 16, or any other time. The Brief Psychiatric Rating Scale (BPRS) is a technician-administered scale developed to measure psychiatric symptoms such as depression, anxiety, hallucinations, and unusual behavior. Each symptom is scored on a range from 1 (not present) to 7 (extremely severe). Zero is entered if the article is not evaluated and will be excluded from the analysis. The scale must be administered by a clinical technician with knowledge of psychiatric disorders and who can interpret the concepts used in the evaluation. Factor 1 (reality distortion) items are lack of confidence, hallucinatory behavior, and unusual thinking. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, eg, for a type of depression, has or is selected for having a Brief Psychiatric Rating Scale (BPRS) score of factor 1. which is the baseline score: at least about 3, at least about 4, at least about 5, at least about 6, about 7, about 3-7, about 4-7, about 4-5, about 5-6 or about 6-7. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in BPRS factor 1 score that is at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, about 0.1-6, about 0.1-1, about 1-2, about 2-3, about 3-4, about 4-5, about 5-6, about 0.1-3 or about 3- 6 compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The treatment effect can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has or is selected for having a Beck Depression Inventory (BDI) score that is at least about 20, at least about 25, at least about 30, at least about 35, at least about 40, at least about 45, at least about 50, at least about 55, at least about 60, about 20-25 , about 25-30, about 30-35, about 35-40, about 40-45, about 45-50, / ^ζοηη / ίζηζ / Β / γι about 50-55, about 55-60, about 60-63, about 25-35, about 35-45, about 45-55, about 55-63, about 25-40, or about 40-63. The Beck Depression Inventory (BDI, BDI-1A, BDI-II) is a self-report inventory of 21 multiple-choice questions to investigate how the subject has been feeling during the past week. Each question has a set of four possible answers, with a range of intensity. In scoring the test, a value from 0 to 3 is assigned to each response, and the total score is then compared to a key to determine the severity of depression. A higher total score indicates more severe depression symptoms. Standard cutoff scores are as follows: 0-9: indicates minimal depression; 10-18: indicates mild depression; 19-29: indicates moderate depression; and 30-63: indicates severe depression. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having a reduction in BDI score that is at least about 10%, at least about 20%, at least about 30%, at least about 40 % or at least approximately 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The effect of treatment can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. In some modalities, the human being treated with a combination of dextromethorphan and bupropion, for example, for a type of depression, has or is selected for having C-reactive protein (CRP) levels that are at least 0.5 mg / L, at less than 1 mg / L, at least 2 mg / L or higher. In some modalities, administration of the combination of dextromethorphan and bupropion results in the human having an improvement in the CRP level that is at least about 10%, at least about 20%, at least about 30%, at least about 40% or at least approximately 50% compared to reference or placebo. In some embodiments, the reduction is compared to the reference. In some modalities, the reduction is compared to placebo. The effect of treatment can be assessed at any suitable time, such as during weeks 1-2, weeks 1-3, weeks 1-4, weeks 1-5, weeks 1-6, weeks 4-6, weeks 6-8, weeks 8-12, weeks 12-16, at the start or end of week 1, at the start or end of week 2, at the start or end of week 3, at the start or end of week 4, at the start or end of week 5, at the start or end of week 6, at the start or end of week 7, at the start or end of week 8, at the start or end of / frZQnn / Lznz / E / Yii from week 9, at the start or end of week 10, at the start or end of week 11, at the start or end of week 12, at the start or end of week 13, at the start or at the end of week 14, at the start or end of week 15, at the start or end of week 16, or at any other time. / frZQnn / Lznz / E / Yii The conversion between some of the scores in some of the above ratings can be done according to the following tables. Severity IDS-C IDS-SR QIDS-C QIDSSR HRSD 17 HRSD21 HRSD24 MADRS BDI 0 0-3 0-3 0 0 0 0-1 0-1 0 0 0 4-5 4-5 1 1 1-2 2 2 0 6 6 2 2 3 3 3-4 0 7-8 7-8 3 3 4 4 5 0 9-10 9-11 4 4 5-6 5-6 6-7 0 11 12-13 5 5 7 7-8 8-9 6 9 1 12-15 14-16 6 6 8 9 10-11 7 10 1 16-17 17-18 7 7 9-10 10 12 1 18-20 19-21 8 8 11 11-12 13- 14 1 21-22 22-23 9 9 12 13 15-16 1 23 24-25 10 10 13 14-15 17-18 19 18 2 24-27 26-28 11 11 14-15 16 19 20 19 2 28- 29 29-30 12 12 16 17 20-21 2 30-32 31-33 13 13 17 18-19 22-23 Severity IDS-C IDS-SR QIDS-C QIDSSR HRSD17 HRSD21 HRSD24 MADRS BDI 2 33-35 34-36 14 14 18-19 20-21 24-25 2 36 37-38 15 15 18-19 22 26 34 29 3 37 -39 39-40 16 16 20 23 27-28 35 30 3 40-41 41-43 17 17 21-22 24-25 29-30 3 42-43 44-45 18 18 23 26 31-32 3 44-45 46-47 19 19 24 27 33 3 46 48 20 20 25 28 34 4 47-51 49-53 21 21 26-27 29-31 35-38 4 52-53 54-55 22 22 28 32 39 4 54-56 56-58 23 23 29 33-34 40-41 4 57-59 59-61 24 24 30-31 35-36 42-44 4 60-62 62-24 25 25 32 37-38 45-46 4 63-65 65-67 26 26 33-35 39-41 47-49 4 66-84 68-84 27 27 36-52 42-64 50-75 60 63 'Severity of depression. 0=None, 1=Medium, 2=Moderate, 3=Severe, 4=Very serious. Severity IDS-SR QIDS-SR HRSD 17 HRSD21 HRSD24 0 0-3 0 0 0-1 0-1 0 4-5 1 1-2 2 2 0 6 2 3 3 3-4 0 7-8 3 4 4 5 5 0 9-11 4 5-6 5-6 6-7 0 12-13 5 7 7-8 8-9 1 14—16 6 8 9 10-11 1 17-18 7 9-10 10 12 1 19-21 8 11 11-12 13-14 10 1 22-23 9 12 13 15-16 1 24-25 10 13 14-15 17-18 2 26-28 11 14-15 16 19 2 29-30 12 16 17 20- 21 2 31-33 13 17 18-19 22-23 2 34-36 14 18-19 20-21 24-25 15 2 37-38 15 18-19 22 26 3 39-40 16 20 23 27-28 3 41 -43 17 21-22 24-25 29-30 3 44-45 18 23 26 31-32 3 46-47 19 24 27 33 3 48 20 25 28 34 20 4 49-53 21 26-27 29-31 35- 38 4 54-55 22 28 32 39 4 56-58 23 29 33-34 40-41 4 59-61 24 30-31 35-36 42-44 4 62-24 25 32 37-38 45-46 4 65- 67 26 33-35 39-41 47-49 25 4 68-84 27 36-52 42-64 50-75 'Severity of depression. O=None, 1=Medium, 2=Moderate, 3=Severe, 4=Very serious. QIDS-SR16 IDS-SR30 HAM-D24 HAM-D21 HAM-D17 0 0-3 0-1 0-1 0 30 1 4-5 2 2 1-2 2 6 3-4 3 3 3 7-8 5 4 4 4 9-11 6-7 5-6 5-6 5 12-13 8-9 7-8 7 6 14-16 10-11 9 8 7 17-18 12 10 9-10 35 8 19-21 13-14 11-12 11 9 22-23 15-16 13 12 10 24-25 17-18 14-15 13 11 26-28 19 16 14-15 12 29-30 20-21 17 16 13 31-33 22-23 18 -19 17 14 34-36 24-25 20-21 18-19 QIDS-SR16 IDS-SR30 HAM-D24 HAM-D21 HAM-D17 15 37-38 26 22 18-19 16 39-40 27-28 23 20 17 41-43 29-30 24-25 21-22 18 44-45 31-32 26 23 19 46-47 33 27 24 20 48 34 28 25 21 49-53 35-38 29-31 26-27 22 54-55 39 32 28 23 56-58 40-41 33-34 29 24 59 -61 42-44 35-36 30-31 25 62-24 45-46 37-38 32 26 65-67 47-49 39-41 33-35 27 68-84 50-75 42-64 36-52 / frZQnn / Lznz / E / Yii IDS-SR30 QIDS-SR16 HAM-D24 HAM-D21 HAM-D17 0-2 0 0 0 0 3 0 1 1 1 4-5 1 2-3 2 2 6 2 4 3 3 7 3 5 4 3 8 3 5 4 4 9 4 6 5 5 10 4 7 6 5 11 4 7 6 6 12 5 8 7 6 13 5 9 7 7 14 6 9 8 7 15 6 10 9 8 16 6 11 9 9 17 7 12 10 9 18 7 12 10 10 19 8 13 11 10 20 8 14 12 11 21 8 15 12 11 22 9 15 13 12 23 9 16 13 12 24 10 17 14 13 25 10 17 15 13 26 11 18 15 14 27 11 19 16 14 28 11 20 16 15 29 12 20 17 15 30 12 21 17 16 31 13 22 18 16 32 13 22 19 17 33 13 23 19 17 34 14 24 20 18 35 14 25 20 19 36 14 25 21 1 9 37-38 15 26 22 20 39- 40 16 27-28 23 20 41 17 29 24 21 IDS-SR30 QIDS-SR16 HAM-D24 HAM-D21 HAM-D17 42-43 17 30 25 22 44-45 18 31-32 26 23 46-47 19 33 27 24 48 20 34 28 25 49-50 21 35 29 26 51-52 21 36-37 30 26 53 21 38 31 27 54-55 22 39 32 28 56-57 23 40 33 29 58 23 41 34 29 59 24 42-43 35 30 60-61 24 44 36 3 1 62 25 45 37 32 63-64 25 46 38 33 65 26 47 39 33 66 26 48 40 34 67 26 49 41 35 68 27 50 42 35 69-70 27 51 43 36 71 27 52 44 37 72 2 7 53-54 45 38 73- 74 27 55 46 39 75-76 27 56 47-48 40 77-78 27 57-58 49-50 42-43 79-82 27 59-62 51-54 44-48 83-84 27 63-75 55-64 49-52 / ^ζοηη / ίζηζ / Β / γι In some modalities, the combination of dextromethorphan and bupropion is a new oral NMDA receptor antagonist with multimodal activity for the treatment of central nervous system (CNS) disorders. Dextromethorphan is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, also known as a glutamate receptor modulator, which is a new mechanism of action that works differently from currently available therapies for depression. . Dextromethorphan is also a sigma-1 receptor agonist, nicotinic-type acetylcholine receptor antagonist, and inhibitor of serotonin and norepinephrine transporters. Bupropion can increase the bioavailability of dextromethorphan and is a norepinephrine and dopamine reuptake inhibitor, as well as a nicotinic-type acetylcholine receptor antagonist. Both dextromethorphan and bupropion are acetylcholine receptor antagonists of the nicotinic type, a mechanism relevant to nicotine dependence. Therefore, the combination of dextromethorphan and bupropion provides a potentially new mechanism of action for smoking cessation treatment. In some modalities, the combination of dextromethorphan and bupropion can be used to treat nicotine addiction. In some embodiments, the combination of dextromethorphan and bupropion can be administered once daily or twice daily to a human. In some embodiments, the combination of dextromethorphan and bupropion can be administered twice daily to a human. In some modalities, the combination of dextromethorphan and bupropion can be administered once daily or twice daily to a human for at least 1 week, at least 2 weeks, at least 3 weeks, at least 5 weeks , at least 6 weeks, at least 1 month, at least 2 months, at least 3 months, at least 4 months, at least 5 months, at least 6-months, about 6-12 months, about 1 year, about 2 years or more. In some embodiments, the combination of dextromethorphan and bupropion can be administered twice daily to a human for at least 1 week, at least 2 weeks, at least 3 weeks, or longer. In some embodiments, the smoker may be or may be selected for being an ad lib smoker. In some embodiments, the smoker may or may be selected for smoking 10 or more cigarettes per day on average, such as approximately approximately approximately 10-20, approximately 14, 18, approximately 10, about 10-15, 11, about 12, 15, about 16, about 10-17, about 13, about 17, about 19, about 20, about 20-25, about 25-30, about 30-40, about 40-50 cigarettes or more, before administration of the combination of dextromethorphan and bupropion. In some modalities, the combination of dextromethorphan and bupropion can be used to treat nicotine addiction and the combination contains approximately 30-100 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, about 70-80 mg, about 80-90 mg, about 90-100 mg, about 35 mg, about 35 mg, about 55 mg, about 65 mg, about 75 mg, about 85 mg or about 95 mg of dextromethorphan in free base form or salt form. In some embodiments, the dextromethorphan is in an HBr salt form. In some embodiments, the combination of dextromethorphan and bupropion can be used to treat addiction to nicotine, wherein the combination contains approximately approximately approximately approximately 100-150 110-120 140-150 170-180 105mg, 135 mg, approximately approximately 165-175 mg, mg, mg, mg, approximately approximately approximately 150-200 120-130 150-160 180-190 mg, mg, mg, mg, approximately approximately approximately approximately 100-200 100-110 130-140 160-170 190-200 mg, mg, mg, mg, mg, approximately 115 mg, approximately 125 mg, approximately 145 mg, approximately 150 mg, approximately 155-165 mg, mg, approximately 175-185 mg or approximately 185-195 mg of bupropion in free base form or salt form. In some embodiments, the bupropion is in an HCI salt form. In some embodiments, administration of the combination of dextromethorphan and bupropion to humans results in a reduction in smoking intensity as measured using the number of cigarettes smoked per day, as assessed by daily recorded smoking diaries. Treatment with the combination of dextromethorphan and bupropion in humans results in a reduction of at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, approximately 5-10%, approximately 10 -15%, about 15-20%, about 20%, about 25-30%, 10-20%, about 20-30%, about 30-40%, about 40-50%, about 50-60%, about 60-80%, approximately 80100%, approximately 20%, approximately 25%, approximately 30%, or approximately 50% greater in the average number of cigarettes smoked per day compared to bupropion alone over a period of time, such as 1 week, 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks, 11 weeks, 12 weeks, 3 months, 4 months, 6 months or more. Treatment with the combination of dextromethorphan and bupropion in humans results in an average reduction of at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 15, at least 20, about 8-9, about 8-10, about 10-15, about 15-20, about 25 or more cigarettes per day. Treatment with the combination of dextromethorphan and bupropion in humans results in a higher proportion of smokers, such as at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55% , at least 60%, at least 65%, at least 70%, about 35%, about 50%, about 60%, about 60-80%, about 80-90%, about 90-100%, experiencing a reduction of more than 50% in expelled carbon monoxide levels, a biochemical marker of smoking intensity, compared with those treated with bupropion alone. Treatment with the combination of dextromethorphan and bupropion in humans results in at least 1 or about 1-2 fewer cigarettes on the day of administration and at least 1, at least 2, about 1-2, or about 2-3 fewer cigarettes. on the following day compared with those who missed one or both doses of the combination of dextromethorphan and bupropion. Smoking cessation treatment with the combination of dextromethorphan and bupropion in humans results in a magnitude of improvement above bupropion alone that is similar to the improvement above placebo reported for the approved varenicline smoking cessation treatment in studies with a similar design. In some embodiments, an enhanced bioavailability of dextromethorphan or a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, may be used as adjunctive therapy to treat any condition indicated herein, including TRD. For example, adjuvant therapy may be used in combination with another antidepressant, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, clomipramine, doxepin, fluoxetine, mianserin, imipramine, 2-chloroimipramine, amitriptyline, amoxapine, desipramine, protriptyline, trimipramine, nortriptyline, maproti lina , phenelzine, isocarboxazid, tranylcypromine, paroxetine, trazodone, citalopram, sertraline, aryloxyindanamine, benactizine, escitalopram, fluvoxamine, venlafaxine, desvenlafaxine, duloxetine, mirtazapine, nefazodone, selegiline, sibutramine, milnacipran, tesofensin, brasofen sina, moclobemide, rasagiline, nialamide, iproniazid , iproclozide, toloxatone, butriptyline, dosulepin, dibenzepine, iprindol, lofepramine, / ^ζοηη / ίζηζ / Β / γι opipramol, norfluoxetine, dapoxetine, ketamine, etc., or a metabolite or prodrug of any of these compounds, or a salt pharmaceutically acceptable of any of these compounds. In some modalities, TRD can be treated with enhanced bioavailability or plasma levels of dextromethorphan, or with a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds and may result in a reduction in symptoms of depression of at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, up to about 100%, or any other reduction in a range bounded by any of these values. Psychiatric disorders that can be treated with enhanced plasma levels of dextromethorphan, such as those obtained with a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, include, without limitation, disorders anxiety disorders, including, without limitation, phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, obsessive-compulsive disorder, and post-traumatic stress disorder (PTSD); mania, manic depressive illness, hypomania, unipolar depression, depression, stress disorders, somatoform disorders, personality disorders, psychosis, schizophrenia, delusional disorder, schizoaffective disorder, schizotypy, aggression, aggression in Alzheimer's disease, agitation and agitation in Alzheimer disease. Agitation in Alzheimer's disease occurs as the disease progresses. Agitation can present as inappropriate verbal, emotional, and / or physical behavior. Inappropriate behavior may include, without limitation, incoherent babbling, inappropriate emotional responses, demands for attention, threats, irritability, frustration, yelling, repetitive questions, mood swings, swearing, abusive language, physical outbursts, emotional distress, restlessness, shredding paper , sleep disorders, delirium, hallucinations, restless walking, wandering, searching, searching objects, repetitive body movement, hoarding, following, hitting, scratching, biting, aggression, hyperactivity and / or kicking. In some modalities, agitation in Alzheimer's disease can be treated with enhanced plasma levels of dextromethorphan or with a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, and may result in a reduction of agitation-related symptoms of at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, up to about 100%, or any other reduction in a range bounded by any of these values. / frZQnn / Lznz / E / Yi Measures of treatment effect that may be enhanced by treatment with improved bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, include , without limitation, Clinical Neuropsychiatric Inventory (NPI-C) scoring scale, overall and all domains; Clinical Neuropsychiatric Inventory (NPI-C) scoring scale, agitation domain; the Cohen-Mansfield Agitation Inventory (CMAI); the Cornell Scale of Depression in Dementia (CSDD); the Neuropsychiatric Inventory (NPI Agitation / Aggression Domain); concomitant medications (frequency of use of concomitant medications); the Alzheimer's Disease Cooperative Study-Activities of Daily Inventory (ADCS-ADL); the Neuropsychiatric Inventory (NPI) Individual domains and NPI total scores (range 0-144), including NPC-C apathy domain, NPI agitated / aggressive caregiver distress, modified Cooperative Study of Alzheimer's Disease - Agitation Clinical Global Impression of Change (agitation mADCS-CGIC), Patient Clinical Global Impression of Change (PGIC) (carer-rated), Dementia Quality of Life (DEMQOL), Quality of Life - measurement of Alzheimer's disease (QoL-AD), Zarit Burden Scale, Resource Utilization in Dementia (RUD), Alzheimer's Disease Rating Scale Cognitive Subscale (ADAS-Cog), Mini Mental State Examination (MMSE), Caregiver Burden Index (CSI), Neuropsychiatric Inventory (NPI) Individual Domain, Neuropsychiatric Inventory (NPI) Total Score, Neuropsychiatric Inventory (NPI Agitation / Aggression Domain), Neuropsychiatric Inventory (Caregiver Distress for NPI Domains), etc. (all of the above for their acronym in English). Substance abuse or addiction that can be treated by bioavailability or enhanced plasma levels of dextromethorphan or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, including, without limitation limitation, drug dependence, cocaine addiction, psychostimulants (eg, crack, cocaine, methamphetamine), nicotine, alcohol, opioids, anti-anxiety and hypnotic drugs, cannabis (marijuana), amphetamines, hallucinogens, volatile solvents, and nitrites volatile Nicotine addiction includes addiction to nicotine in all known forms, such as cigarettes, cigars, and / or pipes, and addiction to chewing tobacco. Disorders of brain function that can be treated with the bioavailability or enhanced plasma levels of dextromethorphan or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, without limitation , disorders involving mental deficits such as senile dementia, Alzheimer's type dementia, memory loss, amnesia / amnestic syndrome, epilepsy, disorders of consciousness, coma, concentration problems, speech disorders, vocal spasms, Parkinson's disease, syndrome Lennox-Gastaut syndrome, autism, hyperkinetic syndrome, and schizophrenia. Disorders of brain function also include disorders caused by cerebrovascular diseases including, without limitation, stroke, cerebral infarction, / ^ζοηη / ίζηζ / Β / γι cerebral hemorrhage, cerebral arteriosclerosis, cerebral venous thrombosis, skull injuries and the like where the Symptoms include impaired consciousness, senile dementia, coma, concentration problems, and slurred speech. Movement disorders that can be treated by improved bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, include, without limitation , akathisia, akinesia, associated movements, athetosis, ataxia, ballismus, hemiballismus, bradykinesia, cerebral palsy, chorea, Huntington's disease, chorea rheumatica, Sydenham's chorea, dyskinesia, tardive dyskinesia, dystonia, blepharospasm, spasmodic torticollis, dystonia responsive to dopamine, Parkinson's disease, restless legs syndrome (RLS), tremors, essential tremors, and Tourette's syndrome and Wilson's disease. Dementias that can be treated by the bioavailability or improved plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, include, without limitation, disease Alzheimer's disease, Parkinson's disease, vascular dementia, Lewy body dementia, mixed dementia, frontotemporal dementia, Creutzfeldt-Jakob disease, normal pressure hydrocephalus, Huntington's disease, Wernicke-Korsakoff syndrome, and Pick's disease. Motor neuron diseases that can be treated by improved bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, but are not limited to limitation, amyotrophic lateral sclerosis (ALS), progressive bulbar palsy, primary lateral sclerosis (PLS), progressive muscular atrophy, post-polio syndrome (PPS), muscular atrophy spinal cord atrophy (SMA), spinal motor atrophy, Tay-Sach disease, Sandoff disease, and hereditary spastic paraplegia. Neurodegenerative diseases that can be treated by the bioavailability or enhanced plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, without limitation, disease Alzheimer's disease, prion-related diseases, cerebellar ataxia, spinocerebellar ataxia (SCA), spinal muscular atrophy (SMA), bulbar muscular atrophy, Friedrich's ataxia, Huntington's disease, Alzheimer's disease, Lewy bodies, Parkinson's disease, amyotrophic lateral sclerosis (ALS, or Lou Gherig's disease), multiple sclerosis (MS), multiple system atrophy, Shy-Drager disease, corticobasal degeneration, progressive supranuclear palsy, Wilson disease, Menkes disease, adrenoleukodystrophy, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), muscular dystrophies, Charcot-Marie-Tooth (CMT) disease ), familial spastic paraplegia, neurofibromatosis, olivopontocerebellar atrophy or degeneration, striatonigral degeneration, Guillain-Barré syndrome, and spastic paraplegia. Seizure disorders that may be treated by improved bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, without limitation, seizures epileptic, nonepileptic seizures, epilepsy, febrile seizures, partial seizures including, without limitation, simple partial seizures, Jacksonian seizures, complex partial seizures, and continuous partial epilepsy; generalized seizures including, without limitation, generalized tonic-clonic seizures, absence seizures, atonic seizures, myoclonic seizures, juvenile myoclonic seizures, and infantile spasms; and status epilepticus. Types of headaches that can be treated by enhanced bioavailability or plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include, without limitation, migraines, tension and cluster headache. Other disorders that can be treated by the bioavailability or enhanced plasma levels of dextromethorphan, or by a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds include Rett syndrome, autism, tinnitus, impaired consciousness disorders, sexual dysfunction, intractable cough, narcolepsy, cataplexy, voice disorders due to uncontrolled spasms of the laryngeal muscles, including, without limitation, abductor spasmodic dysphonia, adductor spasmodic dysphonia, dysphonia due to muscular tension and vocal tremors; diabetic neuropathy, chemotherapy-induced neurotoxicity, such as methotrexate neurotoxicity; incontinence including, without limitation, stress urinary incontinence, urge urinary incontinence, and fecal incontinence; and erectile dysfunction. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to treat pain, joint pain, pain associated with sickle cell disease, affective incontinence, depression (including treatment-resistant depression), memory-related and cognitive disorders, schizophrenia, Parkinson's disease, amyotrophic lateral sclerosis (ALS), Rhett syndrome, seizures, cough (including chronic cough ), etc. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to treat refractory depression. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to treat allodynia. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to treat refractory hyperalgesia. In some embodiments, a combination of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be used to treat dermatitis. The pain relieving properties of dextromethorphan can be enhanced by a method comprising administration of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, with dextromethorphan. The pain relieving properties of bupropion can be enhanced by a method comprising administration of dextromethorphan with bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds. In some embodiments, ketamine or another NMDA receptor antagonist may be administered with an antidepressant, such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, dextromethorphan and quinidine may be co-administered with an antidepressant, such as bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. These methods can be used to treat, or alleviate, any type of pain including, without limitation, musculoskeletal pain, neuropathic pain, cancer-related pain, acute pain, nociceptive pain, inflammatory pain, arthritis pain, complex regional pain syndrome, etc In some modalities, co-administration of dextromethorphan with bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds can be used to treat or reduce inflammation or inflammatory conditions, such as Crohn's disease, including pain associated with inflammation. In some modalities, co-administration of dextromethorphan with bupropion, hydroxybupropion, ethyrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds can be used to treat psoriasis, cancer, viral infections, or as adjuvant treatment for multiple myeloma. Examples of musculoskeletal pain include low back pain (i.e. lumbosacral spinal cord pain), primary dysmenorrhea and arthritis pain, such as pain associated with rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, axial spondyloarthritis including ankylosing spondylitis, pain associated with vertebral compression fractures, fibrous dysplasia, osteogenesis imperfecta, Paget's disease of bone, transient osteoporosis and transient osteoporosis of the hip, etc. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion can be given orally to relieve musculoskeletal pain, including low back pain, / nzonn / i zoz / e / yl, and pain associated with rheumatoid arthritis, juvenile rheumatoid arthritis , osteoarthritis, erosive osteoarthritis, sero-negative (non-rheumatoid) arthropathies, non-articular rheumatism, peri-articular disorders, axial spondyloarthritis including ankylosing spondylitis, Paget's disease, fibrous dysplasia, SAPHO syndrome, transient osteoarthritis of the hip, vertebral fractures due to compression, osteoporosis, etc. In some modalities, a combination of dextromethorphan and an antidepressant such as bupropion can be administered to relieve inflammatory pain including musculoskeletal pain, arthritic pain, and complex regional pain syndrome. Arthritis refers to inflammatory diseases of the joints that may be associated with pain. Examples of arthritis pain include pain associated with osteoarthritis, erosive osteoarthritis, rheumatoid arthritis, juvenile rheumatoid arthritis, sero-negative (non-rheumatoid) arthropathies, non-articular rheumatism, peri-articular disorders, neuropathic arthropathies including Charcot foot, axial spondyloarthritis including spondylitis ankylosing and SAPHO syndrome. In some modalities, a combination of dextromethorphan and an antidepressant, such as bupropion, is used to treat chronic musculoskeletal pain. In some modalities, a combination of dextromethorphan and an antidepressant, such as bupropion, may be given to relieve complex regional pain syndrome, such as complex regional pain syndrome type I (CRPS-I), complex regional pain syndrome type II (CRPS-I), -II), CRPS-NOS or another type of CRPS. CRPS is a type of inflammatory pain. CRPS can also have a neuropathic component. Complex regional pain syndrome is a debilitating pain syndrome. It is characterized by severe pain in an extremity that may be accompanied by edema and autonomic, motor, and sensory changes. In some modalities, a combination of dextromethorphan and an antidepressant, such as bupropion, can be given orally to relieve neuropathic pain. Examples of neuropathic pain include diabetic peripheral neuropathy, postherpetic neuralgia, trigerminal neuralgia, monoradiculopathies, phantom limb pain, central pain, etc. Other causes of neuropathic pain include cancer-related pain, lumbar nerve root compression, spinal cord injuries, post-stroke pain, central multiple sclerosis pain, HIV-associated neuropathy, and radiation- or chemotherapy-associated neuropathy, etc. In some modalities, a combination of dextromethorphan and an antidepressant, such as bupropion, can be given to relieve fibromyalgia. The term "treating" or "treatment" includes the diagnosis, cure, mitigation, treatment, or prevention of disease in humans or other animals, or any other activity that otherwise affects the structure or any function of the human or other animal's body. . Any antidepressant can be used in combination with dextromethorphan to enhance the therapeutic properties of dextromethorphan. Dextromethorphan and the antidepressant compound may be administered in individual compositions or dosage forms, or they may be administered in a single composition or dosage form comprising both. A quinidine can be co-administered with dextromethorphan to provide enhanced plasma levels of dextromethorphan. For a combination of a quinidine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-1000 mg, 1-10 mg, 10 mg, about 5mg, about 4.5, about 1-3mg, about 2-4mg, about 3-5mg, about 4-6mg, about 5-7mg, about 6-8mg, about 7-9mg, about 8-10mg, about 9-11mg, about ΙΟΙ 2mg, about 4.5-5mg, 20mg, 30mg, 30-100mg, about 40mg, about 50mg, about 60mg, about 70mg, about 80 mg, about 90 mg, about 10-30 mg, about 30-50 mg, about 50-70 mg, about 10-90 mg of quinidine, or any dose in a range bounded by any of these values. Antidepressant compounds that may be co-administered with dextromethorphan include, without limitation, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, clomipramine, doxepin, fluoxetine, mianserin, imipramine, 2-chloroimipramine, amitriptyline, amoxapine, desipramine, protriptyline, trimipramine, nortrip tiline, maprotiline, phenelzine, isocarboxazid, tranylcypromine, paroxetine, trazodone, citalopram, sertraline, aryloxy-indanamine, benactizine, escitalopram, fluvoxamine, venlafaxine, desvenlafaxine, duloxetine, mirtazapine, nefazodone, selegiline, sibutramine, milnacipran, tesofensin, brasofensin , moclobemide, rasagiline, nialamide, iproniazide, iproclozide, toloxatone, butriptyline, dosulepin, dibenzepine, iprindol, lofepramine, opipramol, norfluoxetine, dapoxetine, ketamine, etc., or a metabolite or prodrug of any of these compounds, or a pharmaceutically acceptable salt of any of these compounds. For a combination of a ketamine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.01-0.2 mg, approximately 0.2-0.4 mg may be administered. , about 0.4-0.6 mg, about 0.6-0.8 mg, about 0.8-1 mg, about 1-1.2 mg, about 1.2-1.4 mg, about 1.4-1.6 mg, about 1.6-1.8 mg, about 1.8-2 mg, about 2-2.2 mg, approximately / frZQnn / Lznz / E / Yii 2.2-2.4 mg, approximately 2.4-2.6 mg, approximately 16-2.8 1 mg, approximately 2.8-3 mg, approximately 3-3.2 mg, approximately 3.2-3.4 mg, approximately 3.4-3.6 mg, approximately 3.6-3.8 mg, approximately 3.8-4 mg, approximately 3.9-4.1 mg, approximately 4-4.2 mg, approximately 0.2-0.4 mg, approximately 0.2-0.6 mg, approximately 0.2-0.8 mg, approximately 0.2-1 mg, approximately 0.2-1.2 mg, approximately 0.2- 1.4mg, about 0.2-1.6mg, about 0.2-1.8mg, about 0.2-2.0mg, 0.2-2.5mg, about 0.2-3.0mg, about 0.2-3.5mg, about 0.2-4.0 mg, about 5-10 mg, about 10-15 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30-40 mg, about 40-50 mg, about 50 -60 mg, approximately 60-70 mg, approximately 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140mg, about 140-150mg, about 150-160mg, about 160-180mg, about 180-200 mg, about 200-220mg, about 220-240, about 10-500mg, about 50-400mg, about 50-300mg, about 100-250mg, about 1-10mg, about 10-200mg, about 10- 150mg, about 10-100mg, about 10-180mg, about 10-160mg, about 10-140mg, about 10-120mg, about 10-100mg, about 10-20mg, about 20-30mg, about 30 -40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140mg , about 140-160mg, about 160-180mg, about 180-200mg, about 200-220mg, about 220-240, about 240-250mg, about 250-260mg, about 260-280mg, about 280-300mg , about 300-350mg, about 350-400mg, about 25mg, about 50mg, about 100mg, about 250mg, of ketamine, or any dose in a range bounded by any of these values. For a combination of a tesofensine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.2 mg, approximately 0.1-0.3 mg may be administered. , about 0.1-0.4mg, about 0.1-0.5mg, about 0.1-0.6mg, about 0.1-0.7mg, about 0.1-0.8mg, about 0.1-0.9mg, about 0.1-0.1mg, about 0.1-0.12mg, 0.01 -0.2mg, about 0.1-0.3mg, about 0.2-0.4mg, about 0.3-0.5mg, about 0.4-0.6mg, about 0.5-0.7mg, about 0.6-0.8mg, about 0.7-0.9mg, about 0.8-1 mg, approximately 0.9-1.1 mg, of tesofensine, or any dose in a range bounded by any of these values. For a combination of a brasofensin and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.01-0.2 mg, approximately 0.2-0.4 mg may be administered. , about 0.4-0.6 mg, about 0.6-0.8 mg, about 0.8-1 mg, about 1-1.2 mg, about 1.2-1.4 mg, about 1.4-1.6 mg, about 1.6-1.8 mg, about 1.8-2 mg, about 2-2.2 mg, about 2.2-2.4 mg, about 2.4-2.6 mg, about 2.6-2.8 mg, about 2.8-3 mg, / ^ζοηη / ίζηζ / Β / γι about 3-3.2 mg, about 3.2-3.4 mg, about 3.4-3.6 mg, about 3.6-3.8 mg, about 3.8-4 mg, about 3.9-4.1 mg, about 4-4.2 mg, about 0.2-0.4 mg, about 0.2 -0.6mg, about 0.2-0.8mg, about 0.2-1mg, about 0.2-1.2mg, about 0.2-1.4 mg, about 0.2-1.6 mg, about 0.2-1.8 mg, about 0.2-2.0 mg, 0.2-2.5 mg, about 0.2-3.0 mg, about 0.2-3.5 mg, about 0.2-4.0 mg, of brasofensin , or any dose in an interval bounded by / frZQnn / Lznz / E / Yii any of these values. For a combination of a clomipramine and dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 10-500 mg, approximately 50-400 mg , approximately approximately approximately 50-300mg, about 100-250mg, about 1-10mg, 10-200mg, about 10-150mg, about 10-100mg, 10-180mg, about 10-160mg, about 10-140mg, 10-120mg, about 10-100mg, about 10-20mg, about 20-30mg, about 30-40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80 mg, about 80-90 mg, about 90-100 mg, about 100-120 mg, about 120-140mg, about 140-160 mg, about 160-180 mg, about 180-200mg, about 200-220 mg, about 220 -240, about 240-250mg, about 250-260mg, about 260-280mg, about 280-300mg, about 300-350mg, about 350-400mg, about 25mg, about 50mg, about 100mg, about 250 mg, of clomipramine, or any dose in an interval delimited by any of these values. For a combination of a doxepin and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-500 mg, approximately 1-10 mg , about 1-40 mg, about 1-30 mg, about 1-20 mg, about 118 mg, about 1-16 mg, about 1-14 mg, about 1-12 mg, about 1-10 mg, about 10- 150mg, about 10-125mg, about 10-100mg, about 10-75mg, about 10-70mg, about 10-60mg, about 10-50mg, about 10-40mg, about 10-30mg , approximately 10-20 mg, approximately 20-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-220 mg, approximately 220-240, approximately 240-250 mg, about 250-260 mg, about 260-280 mg, about 280-300 mg, about 300-320 mg, about 320-350 mg, about 350-400 mg, about 400-500 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, of the doxepin, or any dose in a range bounded by any of these values. For a combination of a fluoxetine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 5-15 mg , approximately 10-20 mg, approximately 20-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 10 mg, approximately 20 mg, approximately 60 mg, approximately 100 mg , approximately 150 mg, of fluoxetine, or any dose in a range bounded by any of these values. For a combination of a mianserin and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and undeuterium-modified dextromethorphan), a daily dose of approximately 1-300 mg, approximately 1-90 mg , about 1-60 mg, about 1-30 mg, about 1-25 mg, about 120 mg, about 1-15 mg, about 1-10 mg, about 10-20 mg, about 20-30 mg, about 30- 40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140mg , about 140-160 mg, about 160-180 mg, about 180-200 mg, about 30 mg, about 60 mg, about 90 mg, about 120 mg, about 150 mg, of mianserin, or any dose in a limited range for any of these values. For a combination of an imipramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 5-150 mg , approximately 5-125 mg, approximately 5-100 mg, approximately 5-75 mg, approximately 5-60 mg, approximately 5-50 mg, approximately 5-40 mg, approximately 5-30 mg, approximately 5-25 mg, approximately 5-20 mg, about 5-15 mg, about 10-20 mg, about 20-25 mg, about 25-30 mg, about 30-40 mg, about 40-50 mg, about 50-60 mg, about 60-70 mg , approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-220 mg, approximately 220-240, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, about 400-500 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, / ^ζοηη / ίζηζ / Β / γι about 250 mg, about 300 mg, of imipramine, or any dose in an interval bounded by any of these values. For a combination of a 2-chloroimipramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25- 0.5mg, about 0.5-0.75mg, about 0.75-1mg, about 1-5mg, about 5-10mg, about 10-15mg, about 15-20mg, about 20-25mg, about 25-30mg, about 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120- 140mg, about 140-150mg, about 150-160mg, about 160-180mg, about 180-200mg, about 200-220mg, about 220-240, about 240-250mg, about 250-260mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, about 350-400mg, about 400-450mg, about 450-500mg, about 500-550mg, about 550-600mg, about 600-650mg, about 650-700mg, about 700-800mg, about 800-1000mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg , about 400 mg, about 600 mg, of 2-chloroimipramine, or any dose in a range bounded by any of these values. For a combination of an amitriptyline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 5-100 mg , approximately 5-70 mg, approximately 5-60 mg, approximately 5-50 mg, approximately 540 mg, approximately 5-35 mg, approximately 5-30 mg, approximately 5-25 mg, approximately 5-20 mg, approximately 10- 20mg, about 20-30mg, about 30-40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg , approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-220mg, approximately 220-240, approximately 240-250 mg, approximately 250- 260mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, about 350-400mg, about 400-500mg, about 10mg, about 25mg, about 50mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, of amitriptyline, or any dose in a range bounded by any of these values. For a combination of an amoxapine and a dextromethorphan (including deuterium-modified dextromethorphan / ^ζοηη / ίζηζ / Β / γι, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1 -10mg, about 10-20mg, about 10-300mg, about 10-250mg, about 10-200mg, about 10-150mg, about 10-120mg, about 10-100mg, about 10-80 mg, about 10-60 mg, about 10-40 mg, about 20-25 mg, about 25-30 mg, about 30-40 mg, about 40-50 mg, about 50-60 mg, about 60-70 mg, about 70-80 mg, about 80-90 mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 200 -220mg, about 220-240, about 240-250mg, about 250-260mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, about 350-400mg, about 400-500mg, about 500-600mg, about 600-700mg, about 700-800mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg, about 400 mg, of amoxapine, or any dose in a range bounded by any of these values. For a combination of a desipramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 1-15 mg , about 10-20 mg, about 10-25 mg, about 10-30 mg, about 10-40 mg, about 10-50 mg, about 10-60 mg, about 10-70 mg, about 10-80 mg, about 10-90 mg, about 10-100 mg, about 10-120 mg, about 10-140 mg, about 10-150 mg, about 10-180 mg, about 10-200 mg, about 20-30 mg, about 20- 40mg, about 30-40mg, about 40-50mg, about 40-60mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg , approximately 90-110 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 180-220mg, approximately 200-220 mg, approximately 220 -240, about 240-250mg, about 250-260mg, about 260-280mg, about 280-300mg, about 280-320mg, about 300-350mg, about 350-400mg, about 100-200mg, about 25-100 mg, about 25 mg, about 50 mg, about 100 mg, about 200 mg, about 250 mg, of desipramine, or any dose in a range bounded by any of these values. For a combination of a protriptyline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 5-100 mg, approximately 2-5 mg , approximately 2-6 mg, approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 213 mg, approximately 2- 14 mg, approximately 2-15 mg, approximately 2-20 mg, approximately 2-21 mg, approximately 2-22 mg, approximately 2-23 mg, approximately 224 mg, approximately 2-25 mg, approximately 2-26 mg, approximately 2-27 mg, about 2-28 mg, about 2-29 mg, about 2-30 mg, about 235 mg, about 2-40 mg, about 15-60 mg, about 1-5 mg, about 5-10 mg , approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-35 mg, approximately 35-40 mg, approximately 40-45 mg, approximately 45-50 mg, approximately 50-55mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, mg, mg, / ^ζοηη / ίζηζ / Β / γι about 180-200 mg, about 10 mg, about 20 mg, about 30 mg, about 60 mg, about 100 mg, about 150 mg, of the protriptyline, or any dose in a range bounded by any of these values. For a combination of a trimipramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 20-300 mg, approximately 1-10 mg , approximately 5-20 mg, approximately 5-25 mg, approximately 5-30 mg, approximately 535 mg, approximately 5-40 mg, approximately 5-45 mg, approximately 5-50 mg, approximately 5-55 mg, approximately 5- 60mg, about 5-65mg, about 570mg, about 5-75mg, about 5-100mg, about 5-125mg, about 5-150mg, about 10-20mg, about 20-30mg, about 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately approximately approximately approximately approximately 70-80 100-120 140-160 180-220 240-250 280-300mg, 350-400 mg, mg, mg, mg, mg, approximately approximately approximately approximately approximately 80-90 100-200 160-180 200-220 250-260 300-320 mg, about mg, about mg, about mg, about mg, about mg, about 90-100 120-140 180-200 220-240 260-280 320-350 mg, about 400-500 mg, about 10 mg, mg, mg, mg, mg, mg, mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg , approximately 300 mg, of trimipramine, or any dose in a range bounded by any of these values. For a combination of a nortriptyline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 5-10 mg , approximately 5-20 mg, approximately 5-25 mg, approximately 5-30 mg, approximately 535 mg, approximately 5-40 mg, approximately 5-45 mg, approximately 5-50 mg, approximately 5-55 mg, approximately 5- 60mg, about 5-65mg, about 570mg, about 5-75mg, about 5-100mg, about 5-125mg, about 5-150mg, about 10-15mg, about 15-20mg, about 20-25 mg, approximately 20-30 mg, approximately 25-30 mg, approximately 30-35 mg, approximately 30-50 mg, approximately 35-40 mg, approximately 40-45 mg, approximately 45-50 mg, approximately 50- 150mg, about 50-55mg, about 55-60mg, about 60-65mg, about 65-70mg, about 70-80mg, about 80-90mg, about 80-120mg, about 90-100mg , about 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 20 mg, about 30 mg, about 60 mg, about 100 mg , approximately 150 mg, of nortriptyline, or any dose in a range bounded by any of these values. For a combination of a maprotiline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 5-10 mg , approximately 5-20 mg, approximately 5-25 mg, approximately 5-30 mg, approximately 535 mg, approximately 5-40 mg, approximately 5-45 mg, approximately 5-50 mg, approximately 5-55 mg, approximately 5- 60mg, about 5-65mg, about 570mg, about 5-75mg, about 5-100mg, about 5-125mg, about 5-150mg, about 10-15mg, about 10-250mg, about 10-75mg, about 10-50mg, about 15-20mg, about 20-25mg, about 25-30mg, about 30-35mg, about 35-40mg, about 40-45mg, about 45- 50mg, about 50-55mg, about 55-60mg, about 60-65mg, about 60-90mg, about 65-70mg, about 70-75mg, about 75-80mg, about 80-85mg , approximately 80-120 mg, approximately 85-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 100-150 mg, approximately 120-125 mg, approximately 125-140 mg, approximately 140-150 mg, approximately 150-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-225 mg, approximately 210-240 mg, approximately 200-250 mg, approximately 10 mg, approximately 25 mg, approximately 30 mg, approximately 50 mg , about 75 mg, about 100 mg, about 150 mg, about 225 mg, of maprotiline, or any dose in a range bounded by any of these values. For a combination of a phenelzine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), / frZQnn / Lznz / E / Yii may be administered at a daily dose of approximately 1- 5mg, about 5-10mg, about 5-20mg, about 5-25mg, about 5-30mg, about 535mg, about 5-40mg, about 5-45mg, about 5-50mg, about 5-55mg, about 5-60mg, about 5-65mg, about 570mg, about 5-75mg, about 5-90mg, about 10-15mg, about 15-20mg, about 20-25mg , approximately 25-30 mg, approximately 30-35 mg, approximately 35-40 mg, approximately 40-45 mg, approximately 40-50 mg, approximately 45-50 mg, approximately 50-55 mg, approximately 50-70 mg, approximately 50-200mg, about 55-60mg, about 60-65mg, about 60-90mg, about 65-70mg, about 70-80mg, about 80-90mg, 80-120mg, about 90-100 mg, about 100-120 mg, about 100-150 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 15 mg, about 30 mg, about 60 mg, about 100 mg, about 150 mg, of phenelzine, or any dose in a range bounded by any of these values. For a combination of an isocarboxazid and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 2-5 mg , approximately 2-6 mg, approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 213 mg, approximately 2- 14 mg, approximately 2-15 mg, approximately 2-16 mg, approximately 2-17 mg, approximately 2-18 mg, approximately 2-19 mg, approximately 220 mg, approximately 2-21 mg, approximately 2-22 mg, approximately 2-23 mg, approximately 2-24 mg, approximately 2-25 mg, approximately 2-26 mg, approximately 227 mg, approximately 2-28 mg, approximately 2-29 mg, approximately 2-30 mg, approximately 2-35 mg , about 2-40 mg, about 2-45 mg, about 250 mg, about 2-55 mg, about 2-60 mg, about 5-10 mg, about 5-15 mg, about 10-15 mg, about 10- 60mg, about 15-20mg, about 20-25mg, about 25-30mg, about 30-35mg, about 30-50mg, about 35-40mg, about 40-45mg, about 45-50mg , approximately 50-55 mg, approximately 50-70 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 15 mg, about 30 mg, about 60 mg, about 100 mg, about 150 mg, of isocarboxazid, or any dose in an interval bounded by any of these values. For a combination of a tranylcypromine and a dextromethorphan (including deuterium-modified dextromethorphan / frZQnn / Lznz / E / Yi, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1- 5mg, about 1-30mg, about 1-25mg, about 1-20mg, about 2-5mg, about 26mg, about 2-7mg, about 2-8mg, about 2-9mg, about 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 2-13 mg, approximately 2-14 mg, approximately 2-15 mg, approximately 2-16 mg, approximately 217 mg, approximately 2-18 mg , about 2-19 mg, about 2-20 mg, about 2-21 mg, about 2-22 mg, about 2-23 mg, about 224 mg, about 2-25 mg, about 2-26 mg, about 2- 27mg, about 2-28mg, about 2-29mg, about 2-30mg, about 235mg, about 2-40mg, about 2-45mg, about 2-50mg, about 2-55mg, about 2-60 mg, about 5-10 mg, about 10Ι 5 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30-35 mg, about 35-40 mg, about 40-45 mg, about 45-50 mg, about 50-55 mg, about 55-60 mg, about 60-65 mg, about 65-70 mg, about 70-80 mg, about 80-90 mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 15 mg, about 30 mg, about 60 mg, about 100 mg, about 150 mg, of tranylcypromine, or any dose in a range bounded by any of these values. For a combination of a paroxetine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 1-50 mg , about 1-20 mg, about 1-15 mg, about 1-10 mg, about 25 mg, about 2-6 mg, about 2-7 mg, about 2-8 mg, about 2-9 mg, about 2- 10mg, about 2-11mg, about 2-12mg, about 2-13mg, about 2-14mg, about 2-15mg, about 216mg, about 2-17mg, about 2-18mg, about 2-19 mg, approximately 2-20 mg, approximately 2-30 mg, approximately 2-40 mg, approximately 250 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg , approximately 25-30 mg, approximately 30-35 mg, approximately 35-40 mg, approximately 40-45 mg, approximately 45-50 mg, approximately 50-55 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180- 200mg, about 10mg, about 15mg, about 20mg, about 30mg, about 60mg, about 100mg, about / ^ζοηη / ίζηζ / Β / γι 150 mg, of paroxetine, or any dose in an interval delimited by any of these values. For a combination of a trazodone and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 10-20 mg , about 10-30 mg, about 10-40 mg, about 10-50 mg, about 10-60 mg, about 10-70 mg, about 10-80 mg, about 10-90 mg, about 10-100 mg, about 10-120 mg, about 10-140 mg, about 10-150 mg, about 10-180 mg, about 10-200 mg, about 10-250 mg, about 10-300 mg, about 20-25 mg, about 25- 30mg, about 30-40mg, about 40-50mg, about / ^ζοηη / ίζηζ / Β / γι 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-150 mg, approximately 150- 160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-220 mg, approximately 220-240, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, about 300-320 mg, about 320-350 mg, about 350-400 mg, about 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650 -700mg, about 25mg, about 50mg, about mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of trazodone, or any dose in a range bounded by any of these values. For a combination of a citalopram and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 1-20 mg , about 1-15 mg, about 1-10 mg, about 2-5 mg, about 26 mg, about 2-7 mg, about 2-8 mg, about 2-9 mg, about 2-10 mg, about 2- 11mg, about 2-12mg, about 2-13mg, about 2-14mg, about 2-15mg, about 2-20mg, about 225mg, about 2-30mg, about 2-35mg, about 2-40 mg, about 5-10 mg, about 10-15 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30-35 mg, about 35-40 mg, about 40- 45mg, about 45-50mg, about 50-55mg, about 55-60mg, about 60-65mg, about 65-70mg, about 70-80mg, about 80-90mg, about 90-100mg , about 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg , about 60 mg, about 100 mg, approximately 150 mg, of citalopram, or any dose in a range bounded by any of these values. For a combination of a sertraline and dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 1-50 mg , about 1-45 mg, about 1-40 mg, about 1-30 mg, about 120 mg, about 2-5 mg, about 2-6 mg, about 2-7 mg, about 2-8 mg, about 2- 9 mg, approximately 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 2-13 mg, approximately 2-14 mg, approximately 215 mg, approximately 2-16 mg, approximately 2-17 mg, approximately 2-18 mg, approximately 2-19 mg, approximately 2-20 mg, approximately 2-21 mg, approximately 222 mg, approximately 2-23 mg, approximately 2-24 mg, approximately 2-25 mg, approximately 2-26 mg , about 2-27 mg, about 2-28 mg, about 229 mg, about 2-30 mg, about 2-35 mg, about 2-40 mg, about 2-45 mg, about 2-50 mg, about 5- 10 mg, about 10Ι 5 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30-35 mg, about 35-40 mg, about 40-45 mg, about 45-50 mg, about 50-55 mg, about 55-60 mg, about 60-65 mg, about 65-70 mg, about 70-75 mg, about 75-80 mg, about 80-85 mg, about 85-90 mg, about 90 -100 mg, approximately 100-120 mg, approximately 120-125 mg, approximately 125-140 mg, approximately 140-150 mg, approximately 150-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-300 mg, about 10 mg, about 25 mg, about 30 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 200 mg, about 225 mg, of sertraline, or any dose in a range bounded by either of these values. For a combination of an aryloxy indanamine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg, about 0.5-0.75 mg, about 0.75-1 mg, about 1-5 mg, about 5-10 mg, about 10-15 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30 -40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220-240, about 240-250 mg, about 250-260 mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, about 350-400mg, about 400-450mg, about 450-500mg, about 500-550mg, about 550-600mg , about 600-650mg, about 650-700mg, about 700-800mg, about 800-1000mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg , about 400 mg, about 600 mg, of the aryloxy indanamine, or any dose in a range bounded by any of these values. For a combination of a benactizine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120- 140 mg, approximately 140-150 mg, approximately 150-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 200-220 mg, approximately 220-240, approximately 240-250 mg, approximately 250-260 mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, about 350-400mg, about 400-450mg, about 450-500mg, about 500-550mg, about 550-600mg , about 600-650mg, about 650-700mg, about 700-800mg, about 800-1000mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300 mg, about 400 mg, about 600 mg, of benactizine, or any dose in a range bounded by any of these values. For a combination of an escitalopram and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 2-5 mg , approximately 2-6 mg, approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 2-10 mg, approximately 2-12 mg, approximately 2-14 mg, approximately 215 mg, approximately 2- 20mg, about 5-10mg, about 5-15mg, about 10-15mg, about 10-30mg, about 15-20mg, about 15-30mg, about 20-25mg, about 25-30mg , approximately 30-35 mg, approximately 35-40 mg, approximately 40-45 mg, approximately 45-50 mg, approximately 50-55 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, about 80-90 mg, about 90-100 mg, about 100-200 mg, about 5 mg, about 10 mg, about / frZQnn / Lznz / E / Yii mg, about 20 mg, about 25 mg, about 30 mg, about 35 mg, about 40 mg, about 50 mg, of escitalopram, or any dose in a range bounded by any of these values. For a combination of a fluvoxamine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of 50-300 mg, approximately 1-10 mg, may be administered. 10-20 mg, about 10-30 mg, about 10-40 mg, about 10-50 mg, about 10-60 mg, about 10-70 mg, about 10-80 mg, about 10-90 mg, about 10- 100mg, about 10-120mg, about 10-140mg, about 10-150mg, about 10-180mg, about 10-200mg, about 10-250mg, about 10-300mg, about 20-30mg , approximately 30-40 mg, approximately 40-50 mg, approximately 50-60 mg, approximately 60-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 90-110 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 180-220 mg, approximately 200-220 mg, approximately 220-240, approximately 240-250 mg, approximately 240-260 mg, approximately 250-260mg, approximately 260-280 mg, approximately 280-300 mg, approximately 280-320mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400mg, approximately 400- 500 mg, about 10 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, of fluvoxamine, or any dose within a range bounded by any of these values. For a combination of a venlafaxine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 5-20 mg, about 5-25 mg, about 5-30 mg, about 5-35 mg, about 540 mg, about 5-45 mg, about 5-50 mg, about 5-55 mg, about 5-60 mg, about 5-65 mg, about 5-70 mg, about 575 mg, about 5-100 mg, about 5-125 mg, about 5-150 mg, about 10-20 mg, about 20-25 mg, about 25-30 mg, about 30 -40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140 mg, about 140-150 mg, about 120-180 mg, about 150-160 mg, about 160-180mg, about 180-200 mg, about 200-220 mg, about 220-240, about 240-250 mg, about 250 -260mg, about 260-280mg, about 280-300mg, about 300-320mg, about 320-350mg, / frZQnn / Lznz / E / Yii about 350-400mg, about 400-450mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 225, about 250 mg, about 375 mg, about 400 mg, about 600 mg, of venlafaxine, or any dose in an interval bounded by any of these values. For a combination of a desvenlafaxine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 2-5 mg, approximately 2-6 mg , approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 2-13 mg, approximately 2-14 mg, approximately 2-15 mg, about 2-20 mg, about 2-21 mg, about 2-22 mg, about 2-23 mg, about 2-24 mg, about 225 mg, about 2-30 mg, about 2-35 mg , about 2-40 mg, about 2-45 mg, about 2-50 mg, about 2-75 mg, about 2100 mg, about 1-5 mg, about 5-10 mg, about 10-15 mg, about 15- 20mg, about 20-25mg, about 20-30mg, about 25-30mg, about 30-35mg, about 35-40mg, about 40-45mg, about 40-60mg, about 45-50mg , approximately 50-55 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 80-120 mg, approximately 90-100 mg, approximately 100-120 mg, about 120-140 mg, about 140-160 mg, about 160-180 mg, about 180-200 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg, about 60 mg, about 100 mg, about 150 mg, of desvenlafaxine, or any dose in a range bounded by any of these values. For a combination of a duloxetine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 2-5 mg , approximately 2-6 mg, approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 2-10 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 213 mg, approximately 2- 14 mg, approximately 2-15 mg, approximately 2-20 mg, approximately 2-21 mg, approximately 2-22 mg, approximately 2-23 mg, approximately 224 mg, approximately 2-25 mg, approximately 2-26 mg, approximately 2-27 mg, about 2-28 mg, about 2-29 mg, about 2-30 mg, about 235 mg, about 2-40 mg, about 2-45 mg, about 2-60 mg, about 2-90 mg , approximately 2-120 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 20-40 mg, approximately 25-30 mg, approximately 30-35 mg, approximately 30-50mg, approximately 35-40 mg, about 40-45 mg, about 45-50 mg, about 50-55 mg, about 50-70 mg, about 55-60 mg, about 60-65 mg, about / ^ζοηη / ίζηζ / Β / γι 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180- 200 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg, about 60 mg, about 100 mg, about 120 mg, of duloxetine, or any dose within a range bounded by any of these values. For a combination of a mirtazapine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 2-5 mg, approximately 2-6 mg , approximately 2-7 mg, approximately 2-8 mg, approximately 2-9 mg, approximately 210 mg, approximately 2-11 mg, approximately 2-12 mg, approximately 2-13 mg, approximately 2-14 mg, approximately 2- 15mg, about 2-20mg, about 225mg, about 2-30mg, about 2-35mg, about 2-40mg, about 2-45mg, about 1-5mg, about 5-10mg, about 5100 mg, approximately 10-15 mg, approximately 10-50 mg, approximately 15-20 mg, approximately 15-45 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-35 mg, approximately 35-40 mg , approximately 40-45 mg, approximately 45-50 mg, approximately 50-55 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180- 200 mg, approximately 10 mg, approximately 15 mg, approximately 20 mg, approximately 30 mg, approximately 40 mg, approximately 45 mg, approximately 60 mg, approximately 75 mg, of mirtazapine, or any dose within a range bounded by any of these values. For a combination of a nefazodone and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 10-20 mg , about 20-40 mg, about 20-50 mg, about 20-60 mg, about 20-70 mg, about 20-80 mg, about 20-90 mg, about 20-100 mg, about 20-120 mg, about 20-140 mg, about 20-160 mg, about 20-180 mg, about 20- 200mg, about 20-250mg, about 20-300mg, about 20-450mg, about 20-600mg, about 20-25 mg, about 25-30 mg, about 30-40 mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 80-120mg, about 90-100mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 160-240 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-1000 mg, about 1000-1500 mg, / ^ζοηη / ίζηζ / Β / γι about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of nefazodone, or any dose in an interval bounded by any of these values. For a combination of a selegiline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.5-2 mg, approximately 2-5 mg , about 1-10 mg, about 1-9 mg, about 1-8 mg, about 17 mg, about 1-6 mg, about 1-5 mg, about 1-3 mg, about 3-5 mg, about 5- 10mg, about 5-15mg, about 10-15mg, about 15-25mg, about 25-30mg, about 30-35mg, about 35-40mg, about 40-45mg, about 45-50mg , about 5 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg, of selegiline, or any dose in a range bounded by any of these values. For a combination of a sibutramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-5 mg, approximately 1-15 mg , about 1-10 mg, about 1-8 mg, about 5-10 mg, about ΙΟΙ 5 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30-35 mg, about 35 -40mg, about 40-45mg, about 45-50mg, about 50-55mg, about 55-60mg, about 60-65mg, about 65-70mg, about 70-80mg, about 80-90 mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 5 mg, about 10 mg, about 15 mg, about 20 mg, about 30 mg, about 40 mg, about 60 mg, about 100 mg, about 120 mg, of sibutramine, or any dose in a range bounded by any of these values. For a combination of a rasagiline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.3 mg, approximately 0.3-0.5 mg, may be administered. about 0.3-0.7 mg, about 0.5-0.7 mg, about 0.5-1.5 mg, about 0.7-0.9 mg, about 0.9-1.0 mg, about 1.0-1.5 mg, about 1.5-2.0 mg, about 2.0-3.0 mg, about 0.1 mg, about 0.25 mg, about 0.5 mg, about 0.75 mg, about 1 mg, about 2 mg, of rasagiline, or any dose in a range bounded by any of these values. For a combination of a milnacipran and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-7.5 mg, approximately 7.5-12.5 mg may be administered. , about 5-20 mg, about 5-100 mg, about 5-90 mg, about 580 mg, about 5-70 mg, about 5-60 mg, about 5-50 mg, about 5-40 mg, about 12.5- 15mg, about 15-20mg, about 20-30mg, about 20-25mg, about 25-30mg, about 30-35mg, about 35-40mg, about 40-45mg, about 45-50mg , approximately 50-55 mg, approximately 40-60 mg, approximately 55-60 mg, approximately 60-65 mg, approximately 65-70 mg, approximately 70-80 mg, approximately 80-90 mg, approximately 90-100 mg, approximately 80-120 mg, approximately 100-120 mg, approximately 120-140 mg, approximately 140-160 mg, approximately 160-180 mg, approximately 180-200 mg, approximately 180-220 mg, approximately 200-300 mg, approximately 300- 400 mg, about 7.5 mg, about 12.5 mg, about 25 mg, about 50 mg, about 75 mg, about 60 mg, about 100 mg, about 200 mg, of milnacipran, or any dose within a range bounded by any of these values. For a combination of a moclobemide and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 1-10 mg, approximately 10-20 mg , approximately 20-25 mg, approximately 20-450 mg, approximately 20-300 mg, approximately 20-250 mg, approximately 20-200 mg, approximately 20-150 mg, approximately 20-100 mg, approximately 25-30 mg, approximately 30-40mg, about 40-50mg, about 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100mg, about 100-120mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220-240, about 240-250 mg, about 250- 260 mg, approximately 260-280 mg, approximately 280-320 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 430-470 mg, approximately 400-450 mg , about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 25 mg, about 50 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of moclobemide, or any dose in a interval bounded by any of these values. For a combination of a nialamide and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40mg, about 40-50mg, about / frZQnn / Lznz / E / Yii 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of nialamide, or any dose in a range bounded by any of this values. For a combination of an iproniazide and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of iproniazid, or any dose in a range bounded by any of this values. For a combination of an iproclozide and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40mg, about 40-50mg, about / frZQnn / Lznz / E / Yii 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of iproclozide, or any dose within a range bounded by any of this values. For a combination of a toloxatone and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg, about 400 mg, approximately 600 mg, of toloxatone, or any dose in a range bounded by any of these values. For a combination of a butriptyline and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40mg, about 40-50mg, about / frZQnn / Lznz / E / Yi 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of butriptyline, or any dose within a range bounded by any of this values. For a combination of a dosulepin and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of dosulepin, or any dose within a range bounded by any of this values. For a combination of a dibenzepine and a dextromethorphan (including deuterium-modified dextromethorphan, for example, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg, may be administered. about 0.5-0.75 mg, about 0.75-1 mg, about 1 -5 mg, about 5-10 mg, about 10-15 mg, about 15-20 mg, about 20-25 mg, about 25-30 mg, about 30 -40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of dibenzepine, or any dose in a range bounded by any of this values. For a combination of an iprindol and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg, about 400 mg, approximately 600 mg, of iprindol, or any dose in a range bounded by any of these values. For a combination of a lofepramine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40mg, about 40-50mg, about / frZQnn / Lznz / E / Yii 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of lofepramine, or any dose in a range bounded by any of this values. For a combination of an opipramol and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg, about 400 mg, approximately 600 mg, of opipramol, or any dose in a range bounded by any of these values. For a combination of a norfluoxetine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25 mg, about 50 mg, about 75 mg, about 100 mg, about 150 mg, about 250 mg, about 300 mg, about 400 mg, about 600 mg, of norfluoxetine, or any dose in a range bounded by any of this values. For a combination of a dapoxetine and a dextromethorphan (including deuterium-modified dextromethorphan, eg, d6-dextromethorphan, and non-deuterium-modified dextromethorphan), a daily dose of approximately 0.1-0.25 mg, approximately 0.25-0.5 mg may be administered. , approximately 0.5-0.75 mg, approximately 0.75-1 mg, approximately 1 -5 mg, approximately 5-10 mg, approximately 10-15 mg, approximately 15-20 mg, approximately 20-25 mg, approximately 25-30 mg, approximately 30-40 mg, approximately 40-50 mg, approximately 50-60mg, about 60-70mg, about 70-80mg, about 80-90mg, about 90-100 mg, about 100-120 mg, about 120-140 mg, about 140-150 mg, about 150-160 mg, about 160-180 mg, about 180-200 mg, about 200-220 mg, about 220 -240 mg, approximately 240-250 mg, approximately 250-260 mg, approximately 260-280 mg, approximately 280-300 mg, approximately 300-320 mg, approximately 320-350 mg, approximately 350-400 mg, approximately 400-450 mg, about 450-500 mg, about 500-550 mg, about 550-600 mg, about 600-650 mg, about 650-700 mg, about 700-800 mg, about 800-1000 mg, about 25mg, about 50mg, about 75mg, about 100mg, about 150mg, about 250mg, about 300mg, about 400 mg, approximately 600 mg, of dapoxetine, or any dose in a range bounded by any of these values. Bupropion has the structure shown below (the hydrochloride form of bupropion is shown). / bzonn / i znz / E / Yl· Combining bupropion with dextromethorphan may provide greater efficacy, such as greater pain relief, than would otherwise be obtained by administering either component alone. In extensive metabolizers, dextromethorphan can be rapidly and extensively metabolized, providing low systemic exposure even at high doses. In addition to possessing antidepressant and analgesic properties, bupropion is an inhibitor of dextromethorphan metabolism. Bupropion is a dopamine and norepinephrine reuptake inhibitor. It may also be an icotinic-type acetylcholine receptor antagonist and may modulate cytokines associated with inflammatory diseases. Bupropion may affect the levels of tumor necrosis factor alpha and interferon gamma. The metabolites of bupropion, including hydroxybupropion, threohydroxybupropion (also known as threohydrobupropion or threodihydrobupropion), and erythrohydroxybupropion (also known as erythrohydrobupropion or erythrodihydrobupropion) are also inhibitors of dextromethorphan metabolism. Therefore, bupropion, including a form of bupropion that is rapidly converted in the body (as a salt, hydrate, solvate, polymorph, etc.) is a prodrug of hydroxybupropion, threohydroxybupropion, and erythrohydroxybupropion. Bupropion prodrugs can include N-methylbupropion and N-benzylbupropion. As explained above, this inhibition can increase plasma dextromethorphan levels, resulting in additive or synergistic efficacy such as alleviation of neurological disorders including pain, depression, smoking cessation, etc. Therefore, although inhibition of dextromethorphan metabolism is only one of many potential benefits of the combination, co-administration of dextromethorphan with bupropion may thus improve the efficacy of bupropion for many people. Co-administration of dextromethorphan with bupropion may improve the analgesic properties of bupropion for many people. Co-administration of dextromethorphan with bupropion may also improve the analgesic properties of bupropion for many people, including a more rapid onset of action. Another potential benefit of co-administration of dextromethorphan and bupropion is that it may be helpful to reduce the potential for an adverse event, such as somnolence, associated with dextromethorphan treatment. This may be useful, for example, in human patients at risk of experiencing the adverse event as a result of dextromethorphan treatment. Another potential benefit of co-administration of dextromethorphan and bupropion is that it may be helpful to reduce the potential for an adverse event, such as seizures, associated with treatment with bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of these compounds. This may be useful, for example, in human patients at risk of experiencing the adverse event as a result of treatment with bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of these compounds. With respect to dextromethorphan, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of these compounds, co-administration may reduce a central nervous system, gastrointestinal, or other type of adverse event associated with any of these compounds. Central nervous system (CNS) adverse events include, without limitation, nervousness, dizziness, insomnia, lightheadedness, tremors, hallucinations, seizures, CNS depression, fear, anxiety, headache, increased irritability or excitement, tinnitus, somnolence, dizziness, sedation , drowsiness, confusion, disorientation, lassitude, incoordination, fatigue, euphoria, nervousness, insomnia, sleep problems, seizures, excitement, catatonic-like state, hysteria, hallucinations, delirium, paranoia, headache and / or migraines, and extrapyramidal symptoms such as oculogyric crisis , torticollis, hyperexcitability, increased muscle tone, ataxia and / or protrusion of the tongue. Gastrointestinal adverse events include, without limitation, nausea, vomiting, abdominal pain, dysphagia, dyspepsia, diarrhea, bloating, flatulence, peptic ulcers with bleeding, loose stools, constipation, stomach pain, heartburn, gas, loss of appetite, full stomach feeling, indigestion, bloating, hyperacidity, dry mouth, gastrointestinal problems and gastric pain. Co-administration of dextromethorphan and an antidepressant such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds does not necessarily require that the two compounds be administered in the same dosage form. For example, the two compounds can be administered in a single dosage form or they can be administered in two separate dosage forms. Furthermore, the two compounds can be administered at the same time, but it is not required. The compounds can be administered at different times as long as both are within the human body for at least a portion of the time that the treatment is carried out by co-administration. Side effects of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, and / or dextromethorphan may be reduced by administering bupropion, hydroxybupropion, erythrohydroxybupropion, or threohydroxybupropion with dextromethorphan. Examples of side effects that can be reduced include an abnormal sensation of rotation and movement, agitation, pain in the arms, swelling, blurred vision, a burning sensation in the eyes, ringing in the ears, changes in vital signs (including, without limitation, heart rate, respiratory rate, body temperature and blood pressure), feeling cold, constipation, difficulty concentrating, difficulty sleeping, sleep problems, difficulty urinating, difficulty defecating, ear discomfort, ear discomfort eye, stomach discomfort, dizziness, dry lips, dry mouth, dry throat, dysmenorrhea, fatigue, feeling feverish, feeling heavy in the head, feeling unusually agitated, feeling unusually tired, feeling tired, shaky hands, weakness in the hands, headache, heartburn, hot flushes, increased blood pressure, increased skin sensitivity, increased skin sensitivity on the face and head, involuntary muscle contraction, involuntary muscle contraction throughout the body, pain in the knees, weakness in legs, lightheadedness, loose stools, loss of appetite, lower back pain, menstrual disorder, metallic taste, more saliva than normal, mucosal dryness, nasal congestion, nausea, runny nose, feeling of light pressure in the eyes, chills when stretching or yawning, skin sensitivity, skin sensitivity on the arms, face and / or head, difficulty sleeping, soft stools, stomach ache, stomach discomfort, sweaty hands and / or feet, throat irritation, sore throat throat, tinnitus, tremors and / or weakness. Any of these side effects may also be mentioned or grouped according to a corresponding, equivalent, or otherwise relevant term found in the Medical Dictionary for Regulatory Activities (MedRA). In some modalities, co-administration of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds and dextromethorphan results in both bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds and dextromethorphan contributing to the pain relieving properties of the combination. For example, the combination may have improved pain relieving properties compared to bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds alone or compared to dextromethorphan alone, including a potentially faster onset of action. In some modalities, the combination may have enhanced pain relief properties of at least about 0.5%, at least about 1%, at least about 10%, at least about 20%, at least about 30%, at least about 50% , at least 100%, up to about 500% or up to 1000%, about 0.5% to about 1000%, about 10% to about 20%, about 20% to about 30%, about 30% to about 40%, about 40% to approximately 50%, approximately 50% to approximately 60%, approximately 60% to approximately 70%, approximately 70% to approximately 80%, approximately 80% to approximately 90%, approximately 90% to approximately 100%, approximately 100% to approximately 110%, about 110% to about 120%, about 120% to about 130%, about 130% to about 140%, about 140% to about 150%, about 150% to about 160%, about 160% to about 170% , about 170% to about 180%, about 180% to about 190%, about 190% to about 200%, or any amount of / ^ζοηη / ίζηζ / Β / γι pain relief in an interval bounded by or between any of these values, compared to bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds alone. In some modalities, the combination may have enhanced pain relief properties of at least about 0.5%, at least about 1%, at least about 10%, at least about 20%, at least about 30%, at least about 50% , at least 100%, up to about 500% or up to 1000%, about 0.5% to about 1000%, about 10% to about 20%, about 20% to about 30%, about 30% to about 40%, about 40% to approximately 50%, approximately 50% to approximately 60%, approximately 60% to approximately 70%, approximately 70% to approximately 80%, approximately 80% to approximately 90%, approximately 90% to approximately 100%, approximately 100% to approximately 110%, about 110% to about 120%, about 120% to about 130%, about 130% to about 140%, about 140% to about 150%, about 150% to about 160%, about 160% to about 170% , about 170% to about 180%, about 180% to about 190%, about 190% to about 200%, or any amount of pain relief in a range bounded by or between any of these values, compared to dextromethorphan alone. Unless otherwise indicated, any reference herein to a compound, such as dextromethorphan, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, by structure, name, or otherwise, includes pharmaceutically acceptable salts; alternative solid forms, such as polymorphs, solvates, hydrates, etc.; tautomers, deuterium-modified compounds, such as deuterium-modified dextromethorphan; or any chemical species that can be rapidly converted to a compound described herein under the conditions in which the compounds are used, as described herein. In some embodiments, an excess of a bupropion stereoisomer, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, can be administered. In other embodiments, an excess of the S-enantiomer (such as at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 99 % or enantiomerically pure S-enantiomer) or an excess of the R-enantiomer (such as at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95 %, at least 99% or enantiomerically pure R-enantiomer) of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds may be administered. Examples of enantiomerically pure deuterium-enriched bupropion and / or deuterium-enriched bupropion include, without limitation, those listed below. / frZQnn / Lznz / E / Yii / ΐτζοηη / ίζηζ / Ε / γίΛΐ / frZQnn / Lznz / E / YiA In some embodiments, both dextromethorphan and bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds are formulated to be immediate-release, and in other embodiments, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds are formulated to be sustained release. Examples of deuterium-modified dextromethorphan include, without limitation, those listed below. 7b7Qnn / l 7Π7 / Ε / ΥΙΛ d6-dextromethorphan A dosage form or composition can be a combination or mixture of dextromethorphan and a compound that inhibits the metabolism of dextromethorphan, such as bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds, either alone or within a vehicle. For example, dextromethorphan and bupropion can be dispersed within each other or together within a vehicle. A dispersion may include a mixture of solid materials within which individual small particles are substantially a compound, but the small particles are dispersed within them, such as can occur if two powders of two different drugs are mixed with a material of solid carrier and mixing is done in the solid form. In some embodiments, dextromethorphan and bupropion can be substantially uniformly dispersed within a composition or dosage form. Alternatively, dextromethorphan and bupropion may be in different domains or phases within a composition or dosage form. For example, one drug may be in the coating and another drug may be in a core within the coating. For example, one drug can be formulated for sustained release and another drug can be formulated for immediate release. Some modalities include administration of a tablet containing bupropion in a form that provides sustained release and dextromethorphan in a form that provides immediate release. Although there are several ways to achieve sustained release of bupropion, in some embodiments, bupropion is combined with hydroxypropylmethylcellulose. For example, bupropion hydrochloride particles can be mixed with microcrystalline cellulose and hydroxypropylmethylcellulose (eg, METHOCEL®) to form a mixed powder mixture. Subsequently, it can be combined with immediate-release dextromethorphan in a single tablet. Dextromethorphan and / or an antidepressant, such as bupropion, hydroxybupropion, threohydroxybupropion, and erythrohydroxybupropion, or an antidepressant other than bupropion (all of which are collectively referred to herein as "therapeutics" for convenience) may be combined with a pharmaceutical carrier selected with based on the chosen route of administration and standard pharmaceutical practice as described, for example, in Remington's Pharmaceutical Sciences, 2005. The relative proportions of active ingredient and carrier can be determined, for example, by the solubility and chemical nature of the compounds , the chosen route of administration and standard pharmaceutical practice. Therapeutic compounds can be administered by any means that can result in contact of the active agent(s) with the desired site or site(s) of action in the body of a patient. The compounds can be administered by any conventional means available for use in conjunction with pharmaceuticals, either as individual therapeutic agents or in a combination of therapeutic agents. For example, they can be administered as the sole active agent in a pharmaceutical composition or used in combination with other therapeutically active ingredients. Therapeutic compounds can be administered to a human patient in a variety of ways tailored to the chosen route of administration, eg, oral or parenteral. Parenteral administration in this regard includes administration by the following routes: intravenous, intramuscular, subcutaneous, intraocular, intrasynovial, transepithelial including transdermal, ophthalmic, sublingual and buccal; topical including ophthalmic, dermal, ocular, rectal and nasal inhalation via systemic insufflation, aerosol and rectal. / frZQnn / Lznz / E / Yii The ratio of dextromethorphan to bupropion can vary. In some embodiments, the weight ratio of dextromethorphan to bupropion can be about 0.1 to about 10, about 0.1 to about 2, about 0.2 to about 1, about 0.1 to about 0.5, about 0.1 to about 0.3, about 0.2 to about 0.4, about 0.3 to about 0.5, about 0.5 to about 0.7, about 0.8 to about 1, about 0.2, about 0.3, about 0.4, about 0.45, about 0.6, about 0.9, or any ratio in a range bounded by or between any of these values. A ratio of 0.1 indicates that the weight of dextromethorphan is 1 / 10 the weight of bupropion. A ratio of 10 indicates that the weight of dextromethorphan is 10 times the weight of bupropion. The amount of dextromethorphan in a therapeutic composition can vary. For example, some liquid compositions may comprise about 0.0001% (w / v) to about 50% (w / v), about 0.01% (w / v) to about 20% (w / v), about 0.01% to about 10% (w / v), approximately 0.001% (w / v) to approximately 1% (w / v), approximately 0.1% (w / v) to approximately 0.5% (w / v), approximately 1% (w / v) v) to approximately 3% (w / v), approximately 3% (w / v) to approximately 5% (w / v), approximately 5% (w / v) to approximately 7% (w / v), approximately 7 % (w / v) to approximately 10% (w / v), approximately 10% (w / v) to approximately 15% (w / v), approximately 15% (w / v) to approximately 20% (w / v) ), about 20% (w / v) to about 30% (w / v), about 30% (w / v) to about 40% (w / v) or about 40% (w / v) to about 50% (w / v) of dextromethorphan. Some liquid dosage forms may contain about 10mg to about 500mg, about 30mg to about 350mg, about 50mg to about 200mg, about 50mg to about 70mg, about 20mg to about 50mg, about 30mg to about 60 mg, about 40 mg to about 50 mg, about 40 mg to about 55 mg, about 40 mg to about 42 mg, about 42 mg to about 44 mg, about 44 mg to about 46 mg, about 46 mg to about 48 mg, about 48 mg to about 50 mg, about 80 mg to about 100 mg, about 110 mg to about 130 mg, about 170 mg to about 190 mg, about 45 mg, about 60 mg, about 90 mg, about 120 mg or about 180 mg dextromethorphan, or any amount of dextromethorphan in a range bounded by or between any of these values. Some solid compositions may comprise at least approximately 5% (w / w), at least approximately 10% (w / w), at least approximately 20% (w / w), at least approximately 50% (w / w), at least about 70% (w / w), at least about 80%, about 10% (w / w) to about 30% (w / w), about 10% (w / w) to about 20% (w / w ), / ^ζοηη / ίζηζ / Β / γι about 20% (w / w) to about 30% (w / w), about 30% (w / w) to about 50% (w / w), about 30% (w / w) to about 40% (w / w), about 40% (w / w) to about 50% (w / w), about 50% (w / w) to about 80% (w / w) , about 50% (w / w) to about 60% (w / w), about 70% (w / w) to about 80% (w / w) or about 80% (w / w) to about 90% ( w / w) of dextromethorphan. Some solid dosage forms may contain about 10mg to about 500mg, about 30mg to about 350mg, about 20mg to about 50mg, about 30mg to about 60mg, about 40mg to about 50mg, about 40mg to about 42mg, about 42mg to about 44mg, about 44mg to about 46mg, about 46mg to about 48mg, about 48mg to about 50mg, about 50mg to about 200mg, about 50mg to about 70mg, about 80 mg to about 100 mg, about 110 mg to about 130 mg, about 170 mg to about 190 mg, about 60 mg, about 90 mg, about 120 mg, or about 180 mg of dextromethorphan or any amount of dextromethorphan in a limited range by or between any of these values. In some embodiments, the amount of dextromethorphan may range from about 0.1 mg / kg to about 20 mg / kg, about 0.75 mg / kg to about 7.5 mg / kg, about 0.1 mg / kg to about 5 mg / kg, about 0.1 mg / kg to about 3 mg / kg, about 0.3 mg / kg to about 0.9 mg / kg, about 0.3 mg / kg to about 1 mg / kg, about 0.6 mg / kg to about 0.8 mg / kg, about 0.7 mg / kg to about 0.8 mg / kg, about 0.75 mg / kg, about 0.4 mg / kg to about 1.5 mg / kg, about 1 mg / kg to about 2 mg / kg, about 10 mg / kg to about 20 mg / kg, about 12 mg / kg to about 17 mg / kg, about 15 mg / kg to about 20 mg / kg, about 1 mg / kg, about 1 mg / kg to about 10 mg / kg or any value bounded by or between these ranges based on the patient's body weight. The amount of bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds in a therapeutic composition can vary. If it is desired to increase the plasma level of dextromethorphan, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds should be administered in an amount that increases the plasma level of dextromethorphan. For example, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds can be administered in an amount that results in a plasma concentration of dextromethorphan in humans on day 8, day 9, or day 10, which is at least approximately 2 times, at least approximately 5 times, at least approximately 10 times, at least approximately 15 times, at least approximately 20 times, at least approximately 30 times / ^ζοηη / ίζηζ / Β / γι times, at least approximately 40 times, at least about 50 times, at least about 60 times, at least about 70 times, or at least about 80 times the plasma concentration of the same amount of dextromethorphan administered without bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some embodiments, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds can be administered to a human in an amount that results in an area under the curve of 12 hours from time of dosing (AUC0- 12), or a mean human plasma concentration for the 12 hours after dosing (Cmean) of dextromethorphan, on day 8, day 9, or day 10, that is at least 2-fold, at least approximately 5-fold, at least about 10 times, at least about 15 times, at least about 20 times, at least about 30 times, at least about 40 times, at least about 50 times, at least about 60 times, at least about 70 times, or at least about 70 times approximately 80 times the plasma concentration of the same amount of dextromethorphan administered without bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some embodiments, bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds may be administered to a human in an amount that results in a maximum plasma concentration (Cmax) of dextromethorphan in the human, in the day 8, day 9, or day 10, which is at least about 2 times, at least about 5 times, at least about 10 times, at least about 15 times, at least about 20 times, at least about 30 times, or at least about 40 times the plasma concentration of the same amount of dextromethorphan administered without bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion, or a metabolite or prodrug of any of these compounds. For co-administration of bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, an increase in the plasma level of dextromethorphan may occur on the first day that bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite is administered. or prodrug of any of these compounds, compared to the same amount of dextromethorphan administered without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. For example, the plasma level of dextromethorphan on the first day that bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is administered, may be at least about 1.5-fold, at least about at least 2-fold, at least approximately 2.5 times, at least approximately 3 times, at least approximately 4 times, at least approximately 5 times, at least approximately 6 times, at least approximately 7 times, at least approximately 8 times, at least approximately 9 times, or at least approximately 10 times the level that would be obtained by administering the same amount of dextromethorphan given without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the AUC of dextromethorphan on the first day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered, may be at least twice the AUC that would be obtained by administering the same amount of dextromethorphan administered without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the AUC0-12 of dextromethorphan on the first day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 15 ng*h / mL, at least about 17 ng"h / mL, at least about 19 ng"h / mL, at least about 20 ng"h / mL, at least about 22 ng«h / mL, at least approximately 23 ng«h / mL, at least approximately 24 ng«h / mL, at least approximately 25 ng«h / mL, at least approximately 26 ng«h / mL, at least approximately 27 ng«h / mL, at least approximately 28 ng«h / mL, at least approximately 29 ng«h / mL, at least approximately 30 ng«h / mL, at least approximately 31 ng«h / mL, at least approximately 32 ng*h / mL, at least approximately 33 ng*h / mL, at least approximately 34 ng«h / mL, at least approximately 35 ng«h / mL, at least approximately 36 ng«h / mL, at least approximately 37 ng*h / mL, at least approximately 38 ng*h / mL, at least approximately 39 ng«h / mL, at least approximately 40 ng«h / mL, at least approximately 41 ng«h / mL, at least approximately 42 ng»h / mL, at least approximately 43 ng»h / mL, at least approximately 44 ng»h / mL, at least approximately 45 ng«h / mL, at least approximately 46 ng»h / mL, at least approximately 47 ng«h / mL, at least approximately 48 ng«h / mL, at least approximately 49 ng*h / mL, at least approximately 50 ng*h / mL, at least approximately 51 ng«h / mL, at least approximately 52 ng«h / mL, at least approximately 53 ng*h / mL, at least approximately 54 ng«h / mL, at least approximately 55 ng«h / mL, at least approximately 56 ng«h / mL, or at least approximately 56.7 ng«h / mL and can be up to 10,000 ng«h / mL. In some modalities, the AUC0-12 of dextromethorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 40 ng*h / mL, at least about 50 ng"h / mL, at least about 60 ng"h / mL, at least about 70 ng"h / mL, at least about 80 ng«h / mL, at least approximately 90 ng«h / mL, at least approximately 100 ng«h / mL, at least approximately 150 ng«h / mL, at least approximately 200 ng«h / mL, at least approximately 250 ng«h / mL, at least approximately 300 ng«h / mL, at / ^ζοηη / ίζηζ / Β / γι less approximately 350 ng*h / mL, at least approximately 400 ng*h / mL, at least approximately 450 ng «h / mL, at least about 500 ng«h / mL, at least about 550 ng«h / mL, about 500 ng«h / mL to about 600 ng«h / mL, about 500 ng«h / mL to about 550 ng-h / mL, about 500 ng"h / mL to about 525 ng"h / mL, about 525 ng"h / mL to about 600 ng*h / mL, at least about 600 ng"h / mL, at at least about 650 ng"h / mL, at least about 700 ng"h / mL, at least about 750 ng"h / mL, at least about 800 ng"h / mL, about 800 ng"h / mL to about 900 ng «h / mL, approximately 850 ng»h / mL to approximately 900 ng«h / mL, approximately 850 ng»h / mL to approximately 875 ng«h / mL, approximately 875 ng«h / mL to approximately 900 ng«h / mL, approximately 900 ng«h / mL to approximately 1,000 ng«h / mL, approximately 1,000 ng«h / mL to approximately 1,100 ng«h / mL, approximately 1,100 ng«h / mL to approximately 1,200 ng*h / mL , approximately 1,200 ng«h / mL to approximately 1,300 ng*h / mL, approximately 1,300 ng*h / mL to approximately 1,400 ng*h / mL, approximately 1,400 ng«h / mL to approximately 1,500 ng*h / mL, approximately 1,500 ng«h / mL to approximately 1,600 ng«h / mL, approximately 1,600 ng*h / mL to approximately 1,700 ng«h / mL, approximately 1,700 ng«h / mL to approximately 1,800 ng*h / mL, approximately 1,800 ng «h / mL to approximately 2,000 ng«h / mL, at least approximately 850 ng«h / mL, at least approximately 900 ng«h / mL, at least approximately 950 ng«h / mL, at least approximately 1000 ng«h / mL, at least about 1050 ng"h / mL, at least about 1100 ng"h / mL, at least about 1150 ng*h / mL, at least about 1200 ng*h / mL, at least about 1250 ng"h / mL, at least about 1300 ng"h / mL, at least about 1350 ng"h / mL, at least about 1400 ng"h / mL, at least about 1450 ng*h / mL, at least about 1500 ng"h / mL, at least about 1550 ng»h / mL, at least about 1600 ng»h / mL, at least about 1625 ng»h / mL, at least about 1650 ng»h / mL, at least about 1675 ng»h / mL, or at least approximately 1686.3 ng«h / mL and, in some modalities, can be up to approximately 50,000 ng«h / mL. In some modalities, the AUC0-24 of dextromethorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 50 ng*h / mL, at least about 75 ng-h / mL, at least about 100 ng-h / mL, at least about 200 ng-h / mL, at least about 300 ng«h / mL, at least approximately 400 ng*h / mL, at least approximately 500 ng*h / mL, at least approximately 600 ng*h / mL, at least approximately 700 ng*h / mL, at least approximately 800 ng*h / mL, at least approximately 900 ng«h / mL, at least approximately 1000 ng«h / mL, at least approximately 1100 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1400 ng«h / mL, at least approximately 1500 ng«h / mL, at least approximately 1600 ng«h / mL, at least approximately 1700 ng«h / mL, at least approximately 1800 ng«h / mL, at least approximately 1900 ng«h / mL, at least approximately 2000 ng«h / mL, at least approximately 2100 ng«h / mL, at least approximately 2200 ng*h / mL, at least approximately 2300 ng«h / mL, at least approximately 2400 ng«h / mL, at least approximately 2500 ng«h / mL, at least approximately 2600 ng«h / mL, at least approximately 2700 ng«h / mL, at least approximately 2800 ng*h / mL, at least about 1850 ng'h / mL, at least about 2900 ng'h / mL, at least about 2950 ng'h / mL, or at least about 2975.3 ng'h / mL and, in some modalities, it can be up to approximately 100,000 ng*h / mL. In some modalities, the AUCo-nf of dextromethorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 75 ng*h / mL, at least about 100 ng*h / mL, at least about 200 ng*h / mL, at least about 300 ng*h / mL, at least about 400 ng*h / mL, at least approximately 500 ng«h / mL, at least approximately 600 ng«h / mL, at least approximately 700 ng«h / mL, at least approximately 800 ng«h / mL, at least approximately 900 ng*h / mL, at least approximately 1000 ng«h / mL, at least approximately 1100 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1400 ng«h / mL, at least approximately 1500 ng«h / mL, at least approximately 1600 ng«h / mL, at least approximately 1700 ng«h / mL, at least approximately 1800 ng«h / mL, at least approximately 1900 ng«h / mL, at least approximately 2000 ng«h / mL, at least approximately 2100 ng«h / mL, at least approximately 2200 ng*h / mL, at least approximately 2300 ng*h / mL, at least approximately 2400 ng*h / mL, at least approximately 2500 ng*h / mL, at least approximately 2600 ng«h / mL, at least approximately 2700 ng«h / mL, at least approximately 2800 ng«h / mL, at least approximately 2900 ng«h / mL, at least approximately 3000 ng«h / mL, at least approximately 3100 ng«h / mL, at least approximately 3200 ng«h / mL, at least approximately 3300 ng«h / mL, at least approximately 3400 ng'h / mL, at least about 3500 ng'h / mL, at least about 3600 ng*h / mL, at least about 3700 ng*h / mL, at least about 3800 ng'h / mL, at least about 3900 ng«h / mL, at least approximately 4000 ng«h / mL, at least approximately 4100 ng«h / mL, at least approximately 4200 ng«h / mL, at least approximately 4300 ng«h / mL, at least approximately 4400 ng«h / mL, at least approximately 4500 ng«h / mL, at least approximately 4600 ng«h / mL, at least approximately 4700 ng«h / mL, at least approximately 4800 ng«h / mL, at least approximately 4900 ng«h / mL, at least approximately 5000 ng*h / mL, at least approximately 5100 ng*h / mL, at least approximately 5200 ng«h / mL, at least approximately 5300 ng«h / mL, at least approximately 5400 ng«h / mL, at least approximately 5500 ng«h / mL, at least approximately 5600 ng«h / mL, at least approximately 5700 ng«h / mL, at least approximately 5800 ng«h / mL, at least approximately 5900 ng«h / mL, at least approximately 6000 ng«h / mL, at least approximately 6100 ng«h / mL, at least approximately 6200 ng«h / mL, at least approximately 6300 ng«h / mL, at / ^ζοηη / ίζηζ / Β / γι less about 6400 ng*h / mL, at least about 6500 ng*h / mL, at least about 6600 ng«h / mL, at least about 6700 ng«h / mL, at least about 6800 ng «h / mL, at least about 6900 ng«h / mL, at least about 7000 ng«h / mL, at least about 7100 ng«h / mL, at least about 7150 ng-h / mL, at least about 7200 ng »h / mL or at least approximately 7237.3 ng»h / mL and, in some modalities, can be up to approximately 100,000 ng«h / mL. In some modalities, the AUCo 12 of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered, it can be at least about 40 ng"h / mL, at least about 50 ng"h / mL, at least about 60 ng"h / mL, at least about 70 ng"h / mL, at least about 80 ng «h / mL, at least approximately 90 ng«h / mL, at least approximately 100 ng*h / mL, at least approximately 150 ng*h / mL, at least approximately 200 ng«h / mL, at least approximately 250 ng «h / mL, at least approximately 300 ng«h / mL, at least approximately 350 ng«h / mL, at least approximately 400 ng*h / mL, at least approximately 450 ng«h / mL, at least approximately 500 ng «h / mL, at least approximately 550 ng«h / mL, approximately 500 ng«h / mL to approximately 600 ng«h / mL, approximately 500 ng«h / mL to approximately 550 ng«h / mL, approximately 500 ng «h / mL to approximately 525 ng«h / mL, approximately 525 ng«h / mL to approximately 600 ng«h / mL, at least approximately 600 ng*h / mL, at least approximately 650 ng*h / mL, at at least about 700 ng"h / mL, at least about 750 ng"h / mL, at least about 800 ng"h / mL, about 800 ng*h / mL to about 900 ng*h / mL, about 850 ng*h / mL to approximately 900 ng«h / mL, approximately 850 ng*h / mL to approximately 875 ng«h / mL, approximately 875 ng»h / mL to approximately 900 ng«h / mL, approximately 900 ng»h / mL to approximately 1,000 ng'h / mL, approximately 1,000 ng'h / mL to approximately 1,100 ng'h / mL, approximately 1,100 ng'h / mL to approximately 1,200 ng'h / mL, approximately 1,200 ng'h / mL to approximately 1,300 ng«h / mL, approximately 1,300 ng*h / mL to approximately 1,400 ng«h / mL, approximately 1,400 ng«h / mL to approximately 1,500 ng*h / mL, approximately 1,500 ng«h / mL to approximately 1,600 ng «h / mL, approximately 1,600 ng»h / mL to approximately 1,700 ng«h / mL, approximately 1,700 ng«h / mL to approximately 1,800 ng*h / mL, approximately 1,800 ng«h / mL to approximately 2,000 ng«h / mL, at least approximately 850 ng«h / mL, at least approximately 900 ng«h / mL, at least approximately 950 ng«h / mL, at least approximately 1000 ng«h / mL, at least approximately 1050 ng*h / mL, at least approximately 1100 ng*h / mL, at least approximately 1150 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1250 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1350 ng«h / mL, at least approximately 1400 ng«h / mL, at least approximately 1450 ng«h / mL, at least approximately 1500 ng«h / mL, at least approximately 1550 ng«h / mL, at least approximately 1600 ng«h / mL, at least approximately 1625 ng«h / mL, at least approximately 1650 ng«h / mL, at / frZQnn / Lznz / E / Yii less approximately 1675 ng*h / mL or at least about 1686.3 ng*h / mL and, in some embodiments, may be up to about 50,000 ng*h / mL. In some modalities, the AUC0-24 of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 50 ng"h / mL, at least about 75 ng"h / mL, at least about 100 ng"h / mL, at least about 200 ng"h / mL, at least about 300 ng»h / mL, at least approximately 400 ng«h / mL, at least approximately 500 ng«h / mL, at least approximately 600 ng«h / mL, at least approximately 700 ng«h / mL, at least approximately 800 ng*h / mL, at least approximately 900 ng«h / mL, at least approximately 1000 ng«h / mL, at least approximately 1100 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1400 ng*h / mL, at least approximately 1500 ng*h / mL, at least approximately 1600 ng«h / mL, at least approximately 1700 ng«h / mL, at least approximately 1800 ng«h / mL, at least approximately 1900 ng«h / mL, at least approximately 2000 ng«h / mL, at least approximately 2100 ng«h / mL, at least approximately 2200 ng*h / mL, at least approximately 2300 ng«h / mL, at least approximately 2400 ng«h / mL, at least approximately 2500 ng«h / mL, at least approximately 2600 ng«h / mL, at least approximately 2700 ng«h / mL, at least approximately 2800 ng«h / mL, at least about 1850 ng«h / mL, at least about 2900 ng«h / mL, at least about 2950 ng*h / mL, or at least about 2975.3 ng«h / mL and, in some modalities, it can be up to approximately 100,000 ng«h / mL. In some modalities, the AUCo-int of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered can be at least about 75 ng"h / mL, at least about 100 ng"h / mL, at least about 200 ng"h / mL, at least about 300 ng"h / mL, at least about 400 ng *h / mL, at least approximately 500 ng«h / mL, at least approximately 600 ng«h / mL, at least approximately 700 ng«h / mL, at least approximately 800 ng«h / mL, at least approximately 900 ng *h / mL, at least approximately 1000 ng«h / mL, at least approximately 1100 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1400 ng «h / mL, at least approximately 1500 ng«h / mL, at least approximately 1600 ng«h / mL, at least approximately 1700 ng*h / mL, at least approximately 1800 ng*h / mL, at least approximately 1900 ng «h / mL, at least about 2000 ng«h / mL, at least about 2100 ng«h / mL, at least about 2200 ng«h / mL, at least about 2300 ng*h / mL, at least about 2400 ng «h / mL, at least approximately 2500 ng«h / mL, at least approximately 2600 ng«h / mL, at least approximately 2700 ng«h / mL, at least approximately 2800 ng«h / mL, at least approximately 2900 ng «h / mL, at least approximately 3000 ng«h / mL, at least approximately 3100 ng«h / mL, at least approximately 3200 ng«h / mL, at least approximately 3300 ng«h / mL, at least approximately 3400 ng «h / mL, at least approximately 3500 ng«h / mL, at least approximately 3600 ng«h / mL, at least approximately 3700 ng*h / mL, at least approximately 3800 ng«h / mL, at least approximately 3900 ng "h / mL, at least about 4000 ng"h / mL, at least about 4100 ng"h / mL, at least about 4200 ng"h / mL, at least about 4300 ng"h / mL, at least about 4400 ng «h / mL, at least approximately 4500 ng«h / mL, at least approximately 4600 ng*h / mL, at least approximately 4700 ng»h / mL, at least approximately 4800 ng»h / mL, at least approximately 4900 ng »h / mL, at least approximately 5000 ng«h / mL, at least approximately 5100 ng*h / mL, at least approximately 5200 ng«h / mL, at least approximately 5300 ng«h / mL, at least approximately 5400 ng «h / mL, at least approximately 5500 ng«h / mL, at least approximately 5600 ng«h / mL, at least approximately 5700 ng«h / mL, at least approximately 5800 ng«h / mL, at least approximately 5900 ng *h / mL, at least about 6000 ng*h / mL, at least about 6100 ng«h / mL, at least about 6200 ng«h / mL, at least about 6300 ng«h / mL, at least about 6400 ng »h / mL, at least approximately 6500 ng*h / mL, at least approximately 6600 ng«h / mL, at least approximately 6700 ng«h / mL, at least approximately 6800 ng«h / mL, at least approximately 6900 ng «h / mL, at least approximately 7000 ng«h / mL, at least approximately 7100 ng«h / mL, at least approximately 7150 ng«h / mL, at least approximately 7200 ng«h / mL, or at least approximately 7237.3 ng«h / mL and, in some modalities, can be up to approximately 100,000 ng«h / mL. In some modalities, the AUC0-12 of dextromethorphan on the tenth day the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 40 ng"h / mL, at least about 50 ng"h / mL, at least about 60 ng"h / mL, at least about 70 ng"h / mL, at least about 80 ng«h / mL, at least approximately 90 ng«h / mL, at least approximately 100 ng«h / mL, at least approximately 150 ng*h / mL, at least approximately 200 ng«h / mL, at least approximately 250 ng«h / mL, at least approximately 300 ng«h / mL, at least approximately 350 ng«h / mL, at least approximately 400 ng*h / mL, at least approximately 450 ng«h / mL, at least approximately 500 ng«h / mL, at least approximately 550 ng«h / mL, approximately 500 ng«h / mL to approximately 600 ng«h / mL, approximately 500 ng«h / mL to approximately 550 ng«h / mL, approximately 500 ng«h / mL to approximately 525 ng*h / mL, approximately 525 ng*h / mL to approximately 600 ng*h / mL, at least approximately 600 ng«h / mL, at least approximately 650 ng«h / mL, at least about 700 ng«h / mL, at least about 750 ng«h / mL, at least about 800 ng«h / mL, about 800 ng«h / mL to about 900 ng«h / mL, about 850 ng« h / mL to approximately 900 ng«h / mL, approximately 850 ng«h / mL to approximately 875 ng«h / mL, approximately 875 ng«h / mL to approximately 900 ng«h / mL, approximately 900 ng«h / mL to / frZQnn / Lznz / E / Yii approximately 1,000 ng«h / mL, approximately 1,000 ng*h / mL to approximately 1,100 ng«h / mL, approximately 1,100 ng«h / mL to approximately 1,200 ng»h / mL, approximately 1,200 ng«h / mL to approximately 1,300 ng«h / mL, approximately 1,300 ng«h / mL to approximately 1,400 ng«h / mL, approximately 1,400 ng«h / mL to approximately 1,500 ng-h / mL, approximately 1,500 ng«h / mL to approximately 1,600 ng*h / mL, approximately 1,600 ng-h / mL to approximately 1,700 ng*h / mL, approximately 1,700 ng«h / mL to approximately 1,800 ng«h / mL, approximately 1,800 ng» h / mL to approximately 2,000 ng»h / mL, at least approximately 850 ng*h / mL, at least approximately 900 ng»h / mL, at least approximately 950 ng»h / mL, at least approximately 1000 ng«h / mL, at least approximately 1050 ng«h / mL, at least approximately 1100 ng*h / mL, at least approximately 1150 ng«h / mL, at least approximately 1200 ng«h / mL, at least approximately 1250 ng«h / mL, at least approximately 1300 ng«h / mL, at least approximately 1350 ng«h / mL, at least approximately 1400 ng«h / mL, at least approximately 1450 ng«h / mL, at least approximately 1500 ng*h / mL, at least approximately 1550 ng*h / mL, at least approximately 1600 ng«h / mL, at least approximately 1625 ng«h / mL, at least approximately 1650 ng«h / mL, at least approximately 1675 ng«h / mL or at least approximately 1686.3 ng*h / mL and, in some modalities, can be up to approximately 50,000 ng«h / mL. In some modalities, the AUC0-24 of dextromethorphan on the 10th day the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , is administered, can be at least about 50 ng*h / mL, at least about 75 ng*h / mL, at least about 100 ng*h / mL, at least about 200 ng*h / mL, at least about 300 ng»h / mL, at least about 400 ng»h / mL, at least about 500 ng»h / mL, at least about 600 ng»h / mL, at least about 700 ng»h / mL, at least about 800 ng-h / mL, at least about 900 ng'h / mL, at least about 1000 ng'h / mL, at least about 1100 ng'h / mL, at least about 1200 ng'h / mL, at least about 1300 ng«h / mL, at least approximately 1400 ng*h / mL, at least approximately 1500 ng*h / mL, at least approximately 1600 ng«h / mL, at least approximately 1700 ng«h / mL, at least approximately 1800 ng«h / mL, at least approximately 1900 ng«h / mL, at least approximately 2000 ng«h / mL, at least approximately 2100 ng«h / mL, at least approximately 2200 ng«h / mL, at least approximately 2300 ng«h / mL, at least approximately 2400 ng«h / mL, at least approximately 2500 ng«h / mL, at least approximately 2600 ng«h / mL, at least approximately 2700 ng«h / mL, at least approximately 2800 ng*h / mL, at least about 1850 ng*h / mL, at least about 2900 ng*h / mL, at least about 2950 ng*h / mL, or at least about 2975.3 ng*h / mL and, in some modalities , can be up to about 100,000 ng«h / mL. In some modalities, the AUCo-¡mf of dextromethorphan on the tenth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of / frZQnn / Lznz / E / Yi any of these compounds, is administered, can be at least about 75 ng"h / mL, at least about 100 ng"h / mL, at least about 200 ng*h / mL, at least about 300 ng «h / mL, at least approximately 400 ng«h / mL, at least approximately 500 ng«h / mL, at least approximately 600 ng«h / mL, at least approximately 700 ng«h / mL, at least approximately 800 ng -h / mL, at least approximately 900 ng*h / mL, at least approximately 1000 ng«h / mL, at least approximately 1100 ng«h / mL, at least approximately 1200 ng»h / mL, at least approximately 1300 ng »h / mL, at least about 1400 ng»h / mL, at least about 1500 ng«h / mL, at least about 1600 ng*h / mL, at least about 1700 ng«h / mL, at least about 1800 ng «h / mL, at least approximately 1900 ng«h / mL, at least approximately 2000 ng«h / mL, at least approximately 2100 ng«h / mL, at least approximately 2200 ng«h / mL, at least approximately 2300 ng «h / mL, at least approximately 2400 ng«h / mL, at least approximately 2500 ng«h / mL, at least approximately 2600 ng'h / mL, at least approximately 2700 ng*h / mL, at least approximately 2800 ng *h / mL, at least about 2900 ng*h / mL, at least about 3000 ng*h / mL, at least about 3100 ng«h / mL, at least about 3200 ng«h / mL, at least about 3300 ng «h / mL, at least approximately 3400 ng«h / mL, at least approximately 3500 ng«h / mL, at least approximately 3600 ng«h / mL, at least approximately 3700 ng«h / mL, at least approximately 3800 ng «h / mL, at least approximately 3900 ng«h / mL, at least approximately 4000 ng«h / mL, at least approximately 4100 ng«h / mL, at least approximately 4200 ng«h / mL, at least approximately 4300 ng *h / mL, at least approximately 4400 ng*h / mL, at least approximately 4500 ng«h / mL, at least approximately 4600 ng«h / mL, at least approximately 4700 ng»h / mL, at least approximately 4800 ng »h / mL, at least about 4900 ng»h / mL, at least about 5000 ng«h / mL, at least about 5100 ng«h / mL, at least about 5200 ng»h / mL, at least about 5300 ng »h / mL, at least about 5400 ng»h / mL, at least about 5500 ng»h / mL, at least about 5600 ng»h / mL, at least about 5700 ng»h / mL, at least about 5800 ng «h / mL, at least approximately 5900 ng«h / mL, at least approximately 6000 ng*h / mL, at least approximately 6100 ng«h / mL, at least approximately 6200 ng«h / mL, at least approximately 6300 ng «h / mL, at least approximately 6400 ng«h / mL, at least approximately 6500 ng*h / mL, at least approximately 6600 ng«h / mL, at least approximately 6700 ng«h / mL, at least approximately 6800 ng «h / mL, at least approximately 6900 ng«h / mL, at least approximately 7000 ng«h / mL, at least approximately 7100 ng«h / mL, at least approximately 7150 ng«h / mL, at least approximately 7200 ng «h / mL or at least approximately 7237.3 ng*h / mL and, in some modalities, can be up to approximately 100,000 ng«h / mL. In some modalities, the Cmax of dextromethorphan on the first day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered may be at least twice the Cmax that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Cmax of dextromethorphan on the first day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be at least about 1.0 ng / mL, at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 2.5 ng / mL, at least about 3.0 ng / mL, at least about 3.1 ng / mL , at least about 3.2 ng / mL, at least about 3.3 ng / mL, at least about 3.4 ng / mL, at least about 3.5 ng / mL, at least about 3.6 ng / mL, at least about 3.7 ng / mL, at least about 3.8 ng / mL, at least about 3.9 ng / mL, at least about 4.0 ng / mL, at least about 4.1 ng / mL, at least about 4.2 ng / mL, at least about 4.3 ng / mL, at least about 4.4 ng / mL, at least about 4.5 ng / mL, at least about 4.6 ng / mL, at least about 4.7 ng / mL, at least about 4.8 ng / mL, at least about 4.9 ng / mL, at least about 5.0 ng / mL, at least about 5.1 ng / mL, at least about 5.2 ng / mL, at least about 5.3 ng / mL, at least about 5.4 ng / mL, at least about 5.5 ng / mL, at least about 5.6 ng / mL , at least about 5.7 ng / mL, at least about 5.8 ng / mL, at least about 5.9 ng / mL, at least about 6.0 ng / mL, at least about 6.1 ng / mL, at least about 6.2 ng / mL, at least about 6.3 ng / mL, at least about 6.4 ng / mL, at least about 6.5 ng / mL, at least about 6.6 ng / mL, at least about 6.7 ng / mL, at least about 6.8 ng / mL, at least about 6.9 ng / mL, at least about 7.0 ng / mL, at least about 7.1 ng / mL, at least about 7.2 ng / mL, at least about 7.3 ng / mL, at least about 7.4 ng / mL, at least about 7.5 ng / mL, at least about 7.6 ng / mL, at least about 7.7 ng / mL, at least about 7.8 ng / mL, at least about 7.9 ng / mL, at least about 8.0 ng / mL, at least about 8.1 ng / mL , at least about 8.2 ng / mL, at least about 8.3 ng / mL, at least about 8.4 ng / mL, at least about 8.5 ng / mL, at least about 8.6 ng / mL, or at least about 8.7 ng / mL, and, in some modalities, it can be up to approximately 1000 ng«h / mL. In some modalities, the Cmax of dextromethorphan on the eighth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be about 50 ng / mL to about 60 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL , approximately / ^ζοηη / ίζηζ / Β / γι ng / mL to approximately 85 ng / mL, approximately 85 ng / mL to approximately 90 ng / mL, approximately approximately approximately approximately approximately approximately approximately 100 105 115 120 135 140 150 155 ng / mL to approximately 95 ng / mL, approximately 100 ng / mL to approximately 110 ng / mL, approximately 115 ng / mL to approximately 130 ng / mL, approximately 135 ng / mL to approximately 145 ng / mL, approximately 150 ng / mL to approximately 160 ng / mL, approximately 95 ng / mL, ng / mL to approximately 105 ng / mL, ng / mL, approximately 110 ng / mL, ng / mL to approximately 120 ng / mL, ng / mL, approximately 130 ng / mLa ng / mL to approximately 140 ng / mL, ng / mL, approximately 145 ng / mLa ng / mL to approximately 155 ng / mL, ng / mL, approximately 160 ng / mLa / ^ζοηη / ίζηζ / Β / γι approximately 170 ng / mL, about 170 ng / mL to about 200 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL , at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL, at at least about 135 ng / mL, at least about 140 ng / mL, at least about 145 ng / mL, at least about 150 ng / mL, at least about 155 ng / mL, or at least about 158.1 ng / mL, and, in some modalities, it can be up to about 10,000 ng / mL. In some modalities, the Cmax of dextromethorphan on the ninth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be about 50 ng / mL to about 60 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL , about 80 ng / mL to about 85 ng / mL, about 85 ng / mL to about 90 ng / mL, about 90 ng / mL to about 95 ng / mL, about 95 ng / mL to about 100 ng / mL, about 100 ng / mL to about 105 ng / mL, about 105 ng / mL to about 110 ng / mL, about 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to about 135 ng / mL, about 135 ng / mL to about 140 ng / mL, about 140 ng / mL to about 145 ng / mL, about 145 ng / mL to about 150 ng / mL, about 150 ng / mL to about 155 ng / mL, about 155 ng / mL to about 160 ng / mL, about 160 ng / mL to about 170 ng / mL, about 170 ng / mL to about 200 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL, at least about 135 ng / mL, at least about 140 ng / mL, at least about 145 ng / mL, at least about 150 ng / mL, at least about 155 ng / mL, or at least about 158.1 ng / mL, and, in some embodiments, can be up to about 10,000 ng / mL. In some modalities, the Cmax of dextromethorphan on the tenth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be about 50 ng / mL to about 60 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL , about 80 ng / mL to about 85 ng / mL, about 85 ng / mL to about 90 ng / mL, about 90 ng / mL to about 95 ng / mL, about 95 ng / mL to about 100 ng / mL, about 100 ng / mL to approximately 105 ng / mL, approximately 105 ng / mL to approximately 110 ng / mL, approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, approximately 160 ng / mL to approximately 170 ng / mL, approximately 170 ng / mL to approximately 200 ng / mL , at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about / frZQnn / Lznz / E / Yii .0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL, at least about 135 ng / mL, at least about 140 ng / mL, at least about 145 ng / mL, at least about 150 ng / mL, at least about 155 ng / mL, or at least about 158.1 ng / mL and, in some embodiments, may be up to about 10,000ng / mL. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered in an amount that results in a Cmean of dextromethorphan, during the period between two independent and consecutive administrations of dextromethorphan, which is at least least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL , at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL, at least about 135 ng / mL, at least about 140 ng / mL, or at least about 140.5 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL mL to about 50 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to about 85 ng / mL, about 85 ng / mL to about 90 ng / mL, about 90 ng / mL to about 95 ng / mL, about 95 ng / mL to about 100 ng / mL, about 100 ng / mL to about 105 ng / mL, approximately 105 ng / mL to approximately 110 ng / mL, / ^ζοηη / ίζηζ / Β / γι approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, approximately 160 ng / mL to approximately 170 ng / mL, approximately 170 ng / mL to approximately 200 ng / mL and, in some modalities, can be up to approximately 10,000 ng / mL. For example, if dextromethorphan is administered at 8 am and 8 pm on day 1 and no dextromethorphan is administered after 8 am and before 8 pm on day 1, the period between two independent and consecutive administrations of dextromethorphan is from immediately after 8 a.m. to immediately after 8 p.m. on Day 1. In some modalities, the Cmean of dextromethorphan on the eighth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL , at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL , at least about 135 ng / mL, at least about 140 ng / mL, or at least about 140.5 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL to about 50 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to approximately 85 ng / mL, approximately 85 ng / mL to approximately 90 ng / mL, approximately 90 ng / mL to approximately 95 ng / mL, approximately 95 ng / mL to approximately 100 ng / mL, approximately 100 ng / mL to approximately 105 ng / mL, approximately 105 ng / mL to approximately 110 ng / mL, approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to about 130 ng / mL, / ^ζοηη / ίζηζ / Β / γι about 130 ng / mL to about 135 ng / mL, about 135 ng / mL to about 140 ng / mL, about 140 ng / mL to about 145 ng / mL , approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, approximately 160 ng / mL to approximately 170 ng / mL, approximately 170 ng / mL to approximately 200 ng / mL and, in some modalities, can be up to approximately 10,000 ng / mL. The Cmean values ​​reported above may be for the period between two independent and consecutive administrations of dextromethorphan, or if dextromethorphan is administered only once on day 8, the Cmean may be for the 12 hours after the first dose of dextromethorphan. In some modalities, the Cmean of dextromethorphan on the ninth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL , at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL , at least about 135 ng / mL, at least about 140 ng / mL, or at least about 140.5 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL to about 50 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to approximately 85 ng / mL, approximately 85 ng / mL to approximately 90 ng / mL, approximately 90 ng / mL to approximately 95 ng / mL, approximately 95 ng / mL to approximately 100 ng / mL, approximately 100 ng / mLA about 105 ng / mL, about 105 ng / mL to about 110 ng / mL, about 110 ng / mL to about 115 ng / mL, about 115 ng / mL about 120 ng / mL, about 120 ng / mL to about 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, / ^ζοηη / ίζηζ / Β / γι approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, approximately 160 ng / mL to approximately 170 ng / mL, approximately 170 ng / mL to approximately 200 ng / mL and, in some embodiments, can be up to approximately 10,000 ng / mL. The Cmean values ​​reported above may be for the period between two independent and consecutive administrations of dextromethorphan, or if dextromethorphan is administered only once on day 9, the Cmean may be for the 12 hours after the first dose of dextromethorphan. In some modalities, the Cmean of dextromethorphan on the tenth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered can be at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL , at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 120 ng / mL, at least about 125 ng / mL, at least about 130 ng / mL , at least about 135 ng / mL, at least about 140 ng / mL, or at least about 140.5 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL to about 50 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to approximately 85 ng / mL, approximately 85 ng / mL to approximately 90 ng / mL, approximately 90 ng / mL to approximately 95 ng / mL, approximately 95 ng / mL to approximately 100 ng / mL, approximately 100 ng / mL to approximately 105 ng / mL, approximately 105 ng / mL to approximately 110 ng / mL, approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, / ^ζοηη / ίζηζ / Β / γι 100 from about 160 ng / mL to about 170 ng / mL, from about 170 ng / mL to about 200 ng / mL and, in some embodiments, can be up to about 10,000 ng / mL. The Cmean values ​​reported above may be for the period between two independent and consecutive administrations of dextromethorphan, or if dextromethorphan is administered only once on day 10, the Cmean may be for the 12 hours after the first dose of dextromethorphan. The values ​​of the fluctuation index Fl (%) of dextromethorphan can be determined by the equation: (Cmax Cmin) IF(%) = - X 100 C / media In some modalities, the Fl (%) of dextromethorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold or at least 2-fold compared to dextromethorphan given for eight days without potentiation of dextromethorphan plasma level, such as by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Fl (%) of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold or at least 2-fold compared to dextromethorphan given for 9 days without potentiation of dextromethorphan plasma level, such as by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Fl (%) of dextromethorphan on the 10th day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold or at least 2-fold compared to dextromethorphan given for 10 days without potentiation of dextromethorphan plasma level, such as by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Fl (%) of dextromethorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of / frZQnn / Lznz / E / Yii 101 any of these compounds, is less than 100%, less than 50%, less than 40%, less than 30%, about 20-50%, about 20-40%, about 20-30% or any value of Fl ( %) in an interval delimited by any of these values. In some modalities, the Fl (%) of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is less than 100%, less than 50%, less than 40%, less than 30%, about 20-50%, about 20-40%, about 20-30% or any value of Fl (%) in a interval bounded by any of these values. In some modalities, the Fl (%) of dextromethorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is less than 100%, less than 50%, less than 40%, less than 30%, about 20-50%, about 20-40%, about 20-30% or any value of Fl (%) in a interval bounded by any of these values. In some modalities, the Fl (%) of dextrorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold, at least 2-fold, at least 3-fold, at least 4-fold, at least 5-fold, or at least 6-fold compared to dextromethorphan given for eight days without plasma level potentiation, as by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Fl (%) of dextrorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold, at least 2-fold, at least 3-fold, at least 4-fold, at least 5-fold, or at least 6-fold compared with dextromethorphan given for 9 days without plasma level potentiation, as per co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the Fl (%) of dextrorphan on the tenth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is reduced by at least 1.5-fold, at least 2-fold, at least 3-fold, at least 4-fold, at least 5-fold, or at least 6-fold compared to dextromethorphan given for 10 days without plasma level potentiation, as per co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion or a metabolite or prodrug / ^ζοηη / ίζηζ / Β / γι 102 of any of these compounds. In some modalities, the Fl (%) of dextrorphan on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is less than 100%, less than 70%, less than 60%, less than 50%, about 30-70%, about 30-60%, about 30-50% or any value of Fl (%) in a interval bounded by any of these values. In some modalities, the Fl (%) of dextrorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is less than 100%, less than 70%, less than 60%, less than 50%, about 30-70%, about 30-60%, about 30-50% or any value of Fl (%) in a interval bounded by any of these values. In some modalities, the Fl (%) of dextrorphan on the ninth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is less than 100%, less than 70%, less than 60%, less than 50%, about 30-70%, about 30-60%, about 30-50% or any value of Fl (%) in a interval bounded by any of these values. In some modalities, the "trough" level of dextromethorphan (eg, plasma level 12 hours after administration, also referred to herein as "Cmin") on the first day that bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, may be at least twice the trough level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds. In some modalities, the dextromethorphan Cmin on the first day the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, administered can be at least about 0.8 ng / mL, at least about 0.9 ng / mL, at least about 1.0 ng / mL, at least about 1.1 ng / mL, at least about 1.2 ng / mL, at least about 1.3 ng / mL, at least about 1.4 ng / mL, at least about 1.5 ng / mL, at least about 1.6 ng / mL, at least about 1.7 ng / mL, at least about 1.8 ng / mL, at least about 1.9 ng / mL, at least about 2.0 ng / mL, at least about 2.1 ng / mL, at least about 2.2 ng / mL, at least about 2.3 ng / mL, at least about 2.4 ng / mL, at least about 2.5 ng / mL, or at least about approximately 2.5 ng / mL and can be up to approximately 100 ng / mL. / ^ζοηη / ίζηζ / Β / γι 103 In some modalities, the dextromethorphan Cmin on the fifth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered it can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, or at least about 80.9 ng / mL mL and can be up to approximately 10,000 ng / mL. In some modalities, the dextromethorphan Cmin on the sixth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered it can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, or at least about 102.2 ng / mL, and can be up to about 10,000 ng / mL. In some modalities, the dextromethorphan Cmin on the seventh day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion or a metabolite or prodrug of any of these compounds, is administered it can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least / frZQnn / Lznz / E / Yii 104 about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL or at least about 110.6 ng / mL and may be up to about 10,000 ng / mL. In some modalities, dextromethorphan Cmin on the eighth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, administered can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 119.3 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL to about 50 ng / mL, about 50 ng / mL mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to about 85 ng / mL, about 85 ng / mL to about 90 ng / mL, about 90 ng / mL to about 95 ng / mL, about 95 ng / mL to about 100 ng / mL, about 100 ng / mL to about 105 ng / mL, about 105 ng / mL to about 110 ng / mL, approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL , approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mLa / ^ζοηη / ίζηζ / Β / γι 105 from about 160 ng / mL, from about 160 ng / mL to about 170 ng / mL or from about 170 ng / mL to about 200 ng / mL and can be up to about 10,000 ng / mL. In some modalities, the dextromethorphan Cmin on the ninth day that the plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered it can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least about 7.0 ng / mL, at least about 8.0 ng / mL, at least about 9.0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about 45 ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about 85 ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 119.3 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to about 40 ng / mL, about 40 ng / mL to about 50 ng / mL, about 50 ng / mL to about 55 ng / mL, about 55 ng / mL to about 60 ng / mL, about 80 ng / mL to about 90 ng / mL, about 80 ng / mL to about 85 ng / mL, about 85 ng / mL to about 90 ng / mL, about 90 ng / mL to about 95 ng / mL, about 95 ng / mL to about 100 ng / mL, about 100 ng / mL to about 105 ng / mL, about 105 ng / mL to about 110 ng / mL, approximately 110 ng / mL to approximately 115 ng / mL, approximately 115 ng / mL to approximately 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mLa from about 160 ng / mL, from about 160 ng / mL to about 170 ng / mL or from about 170 ng / mL to about 200 ng / mL and can be up to about 10,000 ng / mL. In some modalities, dextromethorphan Cmn on the tenth day that plasma dextromethorphan level is enhanced, for example, by co-administration of dextromethorphan with bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any / ^ζοηη / ίζηζ / Β / γι 106 of these compounds, is administered can be at least about 1.5 ng / mL, at least about 2.0 ng / mL, at least about 3.0 ng / mL, at least about 4.0 ng / mL, at least about 5.0 ng / mL, at least about 6.0 ng / mL, at least / ^ζοηη / ίζηζ / Β / γι about 7.0 ng / mL, at least about 8.0 ng / mL, at least about . 0 ng / mL, at least about 10 ng / mL, at least about 15 ng / mL, at least about 20 ng / mL, at least about 25 ng / mL, at least about 30 ng / mL, at least about 35 ng / mL, at least about 40 ng / mL, at least about ng / mL, at least about 50 ng / mL, at least about 55 ng / mL, at least about 60 ng / mL, at least about 65 ng / mL, at least about 70 ng / mL, at least about 75 ng / mL, at least about 80 ng / mL, at least about ng / mL, at least about 90 ng / mL, at least about 95 ng / mL, at least about 100 ng / mL, at least about 105 ng / mL, at least about 110 ng / mL, at least about 115 ng / mL, at least about 119.3 ng / mL, about 20 ng / mL to about 30 ng / mL, about 30 ng / mL to approximately 40 ng / mL, approximately 40 ng / mL to approximately 50 ng / mL, approximately 50 ng / mL to approximately 55 ng / mL, approximately 55 ng / mL to approximately 60 ng / mL, approximately 80 ng / mL to approximately 90 ng / mL, approximately 80 ng / mL to approximately 85 ng / mL, approximately 85 ng / mL to approximately 90 ng / mL, approximately ng / mL to approximately 95 ng / mL, approximately 95 ng / mL to about 100 ng / mL, about 100 ng / mL to about 105 ng / mL, about 105 ng / mL to about 110 ng / mL, about 110 ng / mL to about 115 ng / mL, about 115 ng / mL to about 120 ng / mL, approximately 120 ng / mL to approximately 130 ng / mL, approximately 130 ng / mL to approximately 135 ng / mL, approximately 135 ng / mL to approximately 140 ng / mL, approximately 140 ng / mL to approximately 145 ng / mL, approximately 145 ng / mL to approximately 150 ng / mL, approximately 150 ng / mL to approximately 155 ng / mL, approximately 155 ng / mL to approximately 160 ng / mL, approximately 160 ng / mL to approximately 170 ng / mL or from about 170 ng / mL to about 200 ng / mL and can be up to about 10,000 ng / mL. In some modalities, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, is administered on the first day of at least two days of dextromethorphan treatment, where a reduction in plasma dextrorphan level occurs on the first day. in which bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds and dextromethorphan are co-administered, compared to the same amount of dextromethorphan administered without bupropion, hydroxybupropion, erythrohydroxybupropion, threohydroxybupropion or a metabolite or prodrug of any of these compounds. For example, the plasma level of dextrorphan on the first day can be reduced by at least 5% compared to the plasma level of dextrorphan that would be obtained by administering the same 107 amount of dextromethorphan without bupropion. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least five consecutive days to a human in need of dextromethorphan treatment, wherein, on the fifth day, the Dextromethorphan plasma level is higher than the dextromethorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for five consecutive days. For example, the plasma level of dextromethorphan on the fifth day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) may be at least 5 times, at least 10 times, at least 20 times, at least 40 times, at least 50 times, at least 60 times, at least 65 times, or up to approximately 500 times the level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for five consecutive days. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least six consecutive days to a human in need of dextromethorphan treatment, wherein, on the sixth day, the Dextromethorphan plasma level is higher than the dextromethorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for six consecutive days. For example, the plasma level of dextromethorphan on the sixth day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) may be at least 5-fold, at least 10-fold, at least 20 times, at least 30 times, at least 50 times, at least 60 times, at least 70 times, at least 75 times, or up to approximately 500 times, the level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for six consecutive days. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least seven consecutive days to a human in need of dextromethorphan treatment, wherein, on the seventh day, the Dextromethorphan plasma level is higher than the dextromethorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for seven consecutive days. For example, the plasma level of dextromethorphan on the seventh day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) may be at least 5 times, at least 10 times, at least 20 times, at least 30 times, at least 50 times, at least 70 times, at least 80 times, at least 90 times, or up to about 500 times, the level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, / ^ζοηη / ίζηζ / Β / γι 108 threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for seven consecutive days. In some modalities, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least eight consecutive days, whereby, on the eighth day, dextromethorphan has a plasma level, eg, at 0 hours, 1 hour, 3 hours, 6 hours or 12 hours after administration, which is at least 5 times, at least 10 times, at least 20 times, at least 30 times, at least 50 times, at least 60 times , at least 70 times, at least 80 times, at least 90 times, at least 100 times, or up to approximately 1,000 times, the plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for eight consecutive days. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least eight consecutive days to a human in need of dextromethorphan treatment, wherein, on the eighth day, the Dextromethorphan plasma level is lower than the dextromethorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for eight consecutive days. For example, the plasma level of dextrorphan on the eighth day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) can be reduced by at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% compared to the plasma level of dextromethorphan that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , for eight consecutive days. In some modalities, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least nine consecutive days, whereby, on the ninth day, dextromethorphan has a plasma level, eg, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration, which is at least at least 5 times, at least 10 times, at least 20 times, at least 30 times, at least 50 times, at least 60 times, at least 70 times, at least 80 times, at least 90 times, at least 100 times, or up to approximately 1,000 times the plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for nine consecutive days. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least nine consecutive days to a human in need of dextromethorphan treatment, wherein, on the ninth day, the Dextrorphan plasma level is lower than the dextrorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any / ^ζοηη / ίζηζ / Β / γι 109 of these compounds, for nine consecutive days. For example, the plasma level of dextromethorphan on the ninth day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) can be reduced by at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% compared to the plasma level of dextrorphan that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , for nine consecutive days. In some modalities, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least ten consecutive days, whereby, on the tenth day, dextromethorphan has a plasma level, eg, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration, which is at least at least 5 times, at least 10 times, at least 20 times, at least 30 times, at least 50 times, at least 60 times, at least 70 times, at least 80 times, at least 90 times, at least 100 times, or up to approximately 1,000 times the plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for ten consecutive days. In some embodiments, bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds is co-administered with dextromethorphan for at least ten consecutive days to a human in need of dextromethorphan treatment, wherein, on the tenth day, the Dextrorphan plasma level is lower than the dextrorphan plasma level that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds, for ten consecutive days. For example, the plasma level of dextrorphan on the tenth day (for example, at 0 hours, 1 hour, 3 hours, 6 hours, or 12 hours after administration) can be reduced by at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% compared to the plasma level of dextrorphan that would be obtained by administering the same amount of dextromethorphan without bupropion, hydroxybupropion, threohydroxybupropion, erythrohydroxybupropion, or a metabolite or prodrug of any of these compounds , for ten consecutive days. In some embodiments, bupropion may be administered to a human in an amount that results in a human AUC0-12 of bupropion on day 8 that is at least about 100 ng hr / mL, at least about 200 ng «h / mL, at least approximately 500 ng«h / mL, at least approximately 600 ng«h / mL, at least approximately 700 ng«h / mL, at least approximately 800 ng«h / mL, at least approximately 900 ng "h / mL, at least about 1,000 ng"h / mL, at least about 1,200 ng*h / mL, at least 1,600 ng*h / mL, or up to about 15,000 ng"h / mL. In some embodiments, bupropion may be administered to a human in an amount that results in a Day 8 human bupropion mean that is at least about 10 ng / mL, at least about 20 ng / mL, mL, at least about 40 ng / mL, at least about 50 ng / mL, at least about 60 ng / mL, at least about 70 ng / mL, / ^ζοηη / ίζηζ / Β / γι 110 at least about 80 ng / mL, at least about 90 ng / mL, at least about 100 ng / mL, at least 120 ng / mL, or up to about 1,500 ng / mL. In some embodiments, bupropion can be administered to a human in an amount that results in a human bupropion Cmax on day 8 that is at least about 10 ng / mL, at least about 20 ng / mL, at least about 50 ng / mL, at least about 90 ng / mL, at least about 100 ng / mL, at least about 110 ng / mL, at least about 120 ng / mL, at least about 130 ng / mL, at least about 140 ng / mL, at least 200 ng / mL, or up to about 1,500 ng / mL. Some liquid compositions may comprise approximately 0.0001% (w / v) to approximately 50% (w / v), approximately 0.01% (w / v) to approximately 20% (w / v), approximately 0.01% to approximately 10% (w / v), approximately 1% (w / v) to approximately 3% (w / v), approximately 3% (w / v) to approximately 5% (w / v), approximately 5% (w / v) to approximately 7% (w / v), approximately 5% (w / v) to approximately 15% (w / v), approximately 7% (w / v) to approximately 10% (w / v), approximately 10% (w / v) v) to approximately 15% (w / v), approximately 15% (w / v) to approximately 20% (w / v), approximately 20% (w / v) to approximately 30% (w / v), approximately 30 % (w / v) to about 40% (w / v), or about 40% (w / v) to about 50% (w / v) of bupropion, or any amount of bupropion in a range bounded by or between any of these values. Some liquid dosage forms may contain about 10mg to about 1000mg, about 50mg to about 1000mg, about 10mg to about 50mg, about 50mg to about 100mg, about 40mg to about 90mg, about 200mg to about 300 mg, about 70 mg to about 95 mg, about 100 mg to about 200 mg, about 100 mg to about 110 mg, about 105 mg to about 200 mg, about 110 mg to about 140 mg, about 180 mg to about 220 mg, about 280 mg to about 320 mg, about 105 mg, about 200 mg, about 150 mg or about 300 mg of bupropion, for example, bupropion chloride, or any amount of bupropion in a range bounded by or between any of these values. Some solid compositions may comprise at least approximately 5% (w / w), at least approximately 10% (w / w), at least approximately 20% (w / w), at least approximately 50% (w / w), at least about 70% (w / w), at least about 80%, about 10% (w / w) to about 30% (w / w), about 10% (w / w) to about 20% (w / w ), about 20% (w / w) to about 30% (w / w), about 30% (w / w) to about 50% (w / w), about 30% (w / w) to about 40% (w / w), about 40% (w / w) to about 50% (w / w), about 50% (w / w) to about 80% (w / w), about 50% (w / w) to about 60% (w / w), about 70% (w / w) to about 80% (w / w), or about 80% (w / w) to / ^ζοηη / ίζηζ / Β / γι 111 about 90% (w / w) bupropion, or any amount of bupropion in a range bounded by or between any of these values. Some solid dosage forms may contain about 10mg to about 1000mg, about 50mg to about 1000mg, about 10mg to about 50mg, about 50mg to about 100mg, about 40mg to about 90mg, about 200mg to about 300mg, about 70mg to about 95mg, about 100mg to about 200mg, about 100mg to about 120mg, about 105mg to about 200mg, about 90mg to about 120mg, about 100mg to about 110mg, about 110 mg to about 140 mg, about 50 mg to about 150 mg, about 180 mg to about 220 mg, about 280 mg to about 320 mg, about 105 mg, about 200 mg, about 150 mg, or about 300 of bupropion, for example, bupropion chloride, or any amount of bupropion in a range bounded by or between any of these values. In some modalities, bupropion is administered at a dose that results in a bupropion plasma level of approximately 0.1 μΜ to approximately 10 μΜ, approximately 0.1 μΜ to approximately 5 μΜ, approximately 0.2 μΜ to approximately 3 μΜ, approximately 0.1 μΜ to approximately 1 μΜ, approximately 0.2 μΜ to approximately 2 μΜ, approximately 1 μΜ to approximately 10 μΜ, approximately 1 μΜ to approximately 5 μΜ, approximately 2 μΜ to approximately 3 μΜ, or approximately 2.8 μΜ to approximately 3 μΜ, approximately 1.5 μΜ to approximately 2 μΜ , approximately 4.5 μΜ to approximately 5 μΜ, approximately 2.5 μΜ to approximately 3 μΜ, approximately 1.8 μΜ, approximately 4.8 μΜ, approximately 2.9 μΜ, approximately 2.8 μΜ, or any plasma level in a range bounded by or between any of these values. In some modalities, bupropion, hydroxybupropion, or a prodrug of hydroxybupropion is administered at a dose that results in a plasma hydroxybupropion level of approximately 0.1 μΜ to approximately 10 μΜ, approximately 0.1 μΜ to approximately 5 μΜ, approximately 0.2 μΜ to approximately 3 μΜ, approximately 0.1 μΜ to approximately 1 μΜ, approximately 0.2 μΜ to approximately 2 μΜ, 1 μΜ to approximately 10 μΜ, approximately 1 μΜ to approximately 5 μΜ, approximately 2 μΜ to approximately 3 μΜ, or approximately 2.8 μΜ to approximately 3 μΜ, approximately 1.5 μΜ to approximately 2 μΜ, approximately 4.5 μΜ to approximately 5 μΜ, approximately 2.5 μΜ to approximately 3 μΜ, approximately 1.8 μΜ, approximately 4.8 μΜ, approximately 2.9 μΜ, approximately 2.8 μΜ or any plasma level in an interval bounded by or between any of this values. In some embodiments, bupropion, hydroxybupropion, or a prodrug of hydroxybupropion may be administered to a human in an amount that results in an AUC0-12 of hydroxybupropion in the human, on day 8, which is at least about 3,000 ng / hr. / mL, at least approximately 112 7,000 ng«h / mL, at least approximately 10,000 ng«h / mL, at least approximately 15,000 ng«h / mL, at least approximately 20,000 ng*h / mL, at least approximately 30,000 ng«h / mL, up to approximately 50,000 ng«h / mL, up to approximately 150,000 ng«h / mL or any AUC in a range bounded by or between any of these values. In some embodiments, bupropion, hydroxybupropion, or a prodrug of hydroxybupropion can be administered to a human in an amount that results in a Cmax of hydroxybupropion in the human, on day 8, that is at least about 300 ng / mL, at at least about 700 ng / mL, at least about 1,000 ng / mL, at least about 1,500 ng / mL, at least about 2,000 ng / mL, at least about 4,000 ng / mL, up to about 10,000 ng / mL, up to about 50,000 ng / mL or any Cmax in an interval bounded by or between any of these values. In some embodiments, bupropion, hydroxybupropion, or a prodrug of hydroxybupropion may be administered to a human in an amount that results in a Cmean human hydroxybupropion on day 8 that is at least about 200 ng / mL, at at least about 300 ng / mL, at least about 700 ng / mL, at least about 1,000 ng / mL, at least about 1,500 ng / mL, at least about 2,000 ng / mL, at least about 4,000 ng / mL, up to about 10,000 ng / mL, up to approximately 50,000 ng / mL or any C mean in the range bounded by or between any of these values. In some modalities, bupropion, threohydroxybupropion, or a prodrug of threohydroxybupropion is administered at a dose that results in a plasma threohydroxybupropion level of approximately 0.1 μΜ to approximately 10 μΜ, approximately 0.1 μΜ to approximately 5 μΜ, approximately 0.2 μΜ to approximately 3 μΜ, about 0.1 μΜ to about 1 μΜ, about 0.2 μΜ to approximately 2 μΜ, approximately 1 μΜ to approximately 10 μΜ, approximately μΜ to approximately 5 μΜ, approximately 2 μΜ t...

Claims

1. A method for rapidly relieving the symptoms of depression, comprising administering a combination of bupropion and dextromethorphan once or twice daily to a human being in need, wherein the human experiences a therapeutic effect within 2 weeks of the first day the bupropion and dextromethorphan combination was administered.

2. A method for treating depression, comprising administering a combination of bupropion and dextromethorphan once or twice daily to a human being in need, wherein the human being is of Asian descent.

3. Use of a combination of bupropion and dextromethorphan in the preparation of a medicament for the rapid relief of the symptoms of depression, wherein the medicament is administered once or twice daily to achieve the therapeutic effect within 2 weeks from the first day the medicament was administered.

4. Use of a combination of bupropion and dextromethorphan in the preparation of a drug for the treatment of depression, wherein the drug is administered once or twice daily to a human of Asian descent.

5. The method according to claim 1 or 2 or the use according to claim 3 or 4, wherein the human being is of Japanese descent.

6. The method according to claim 1 or 2 or the use according to claim 3 or 4, wherein the human being is of Chinese descent.

7. The method according to claim 1 or 2 or the use according to claim 3 or 4, wherein the human being is of Korean descent.

8. The method or use according to claim 1, 2, 3, 4, 5, 6 or 7, wherein: approximately 105 mg of bupropion hydrochloride or a molar equivalent amount of: 1) another form of bupropion salt or a 2) free base form of bupropion, is administered orally once or twice daily.

9. The method or use according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein: approximately 44 mg to approximately 46 mg of dextromethorphan hydrobromide, or a molar equivalent amount of: 1) another form of dextromethorphan salt or a 2) free base form of dextromethorphan, is administered orally once or twice daily.

10. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the human being previously had an inadequate response to at least one antidepressant therapy.

11. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein depression is major depressive disorder.

12. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the depression is treatment-resistant depression.

13. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the combination of bupropion and dextromethorphan is administered once or twice daily for at least 30 days.

14. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the combination of bupropion and dextromethorphan is administered once or twice daily for at least 42 days.

15. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14, wherein administration of the bupropion and dextromethorphan combination results in a reduction of the MADRS score by at least 10% compared to the reference.

16. The method or use according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein administration of the bupropion and dextromethorphan combination results in a reduction of the MADRS score of at least 10% compared to placebo.