The study of the clinical course of methamphetamine (MAP) psychosis yields insights into the biological aspect of the relapse of the paranoid psychotic state with hallucination in schizophrenia. A series of MAP psychosis studies in Japan conducted over a period of more than four decades revealed three types of clinical courses of MAP psychosis after discontinuation of MAP: transient type, prolonged type, and persistent type. Identification of the latter two indicates a lasting change in the brain that produces and maintains a schizophrenia-like paranoid psychotic state without MAP. The characteristic course seen in the transient type is acute recurrence of the psychotic state after a long remission period, almost identical to the initial episode, due to reuse of MAP or to psychological stressors. Such lasting vulnerability of the brain to schizophrenia-like psychotic symptoms may be caused by a lasting sensitization of the brain to the psychotogenic action of MAP resulting from its chronic abuse. Experimental studies using animals sensitized to MAP-induced stereotypy suggest that lasting enhancement of MAP-induced dopamine release in the striatum and nucleus accumbens is related to the development and expression of brain vulnerability to schizophrenic symptoms.