Studies of Amphetamine or Methamphetamine Psychosis in Japan: Relation of Methamphetamine Psychosis to Schizophrenia

There exist clinical characteristics of methamphetamine (MAP) psychosis in the Japanese population. MAP psychosis involves paranoid‐hallucinatory states indistinguishable from paranoid schizophrenia, with residual volitional disturbances (e.g., loss of spontaneity and idleness). Paranoid‐hallucinatory states persist after the pharmacological effects of MAP have worn off and readily reappear upon a reinjection of MAP. Individuals with a history of MAP psychosis further undergo spontaneous recurrence of their paranoid‐hallucinatory states in response to stress. The development of MAP psychosis might therefore be related to persisting brain damage or changes in brain metabolism induced by repeated MAP use, and thus studies of the clinical course and neurological basis of MAP psychosis could provide insights into the pathophysiology of schizophrenia. Accordingly, psychiatrists have studied the clinical characteristics of MAP psychosis and examined the neurobiological basis of MAP‐induced behavioral sensitization, using animals. MAP‐induced behavioral sensitization might well be related to dopamine supersensitivity; however, the contribution of presynaptic autoreceptors remains controversial, and other hypotheses should be considered. Recently, the process that triggers spontaneous recurrence of MAP psychosis (flashbacks) and corresponding peripheral neurotransmitter functions has been studied. Stress sensitization associated with noradrenergic hyperactivity, involving increased dopamine release, appears to be crucial in the development of flashbacks. Overall, MAP‐induced susceptibility to paranoid‐hallucinatory states and to abnormal behavior (e.g., stereotyped behavior) in animals is examined as a model for predicting relapses of paranoid schizophrenia. Further extensive studies on the neurobiological and molecular mechanisms of this susceptibility are required.