To investigate further the roles of the RGS9 gene in the pathophysiology of psychosis and drug-taking behaviors, we examined the association of the RGS9 gene with several clinical phenotypes of methamphetamine dependence and psychosis, i.e., the age at first consumption of methamphetamine, latency to onset of psychosis after abuse, prognosis of psychosis after therapy, spontaneous relapse even without reconsumption of methamphetamine, and multiple substance abuse status, which show individual variation and may in part be regulated genetically. Here, RGS9 is linked to substance abuse.