The present invention provides for methods of treating obsessive-compulsive disorder (OCD) and OCD-related disorders (body dysmorphic disorder, hoarding disorder, trichotillomania (hair-pulling disorder), excoriation (
skin-picking) disorder, substance / medication-induced obsessive-compulsive and
related disorder, obsessive- compulsive and
related disorder due to another medical condition, and other specified and unspecified obsessive-compulsive and related disorders), Tic disorders including
Tourette syndrome,
autism spectrum disorder (ASD) and glutamate
excitotoxicity related disorders including
amyotrophic lateral sclerosis (ALS), Parkinson's
disease,
traumatic brain injury,
multiple sclerosis, Huntington's
disease, and
schizophrenia, comprising the step of administering an effective amount of a
histamine type 1
receptor agonist and / or
histamine type 3
receptor antagonist, such as betahistine or its pharmaceutically acceptable salts, analogs, metabolites, prodrugs, derivatives, metabolites, co-crystals, modifications, solvates, hydrates, isotopes, tautomers, esters, polymorphs or stereoisomers.