The prevalence of psychotic symptoms among methamphetamine users

AIMS: To examine the prevalence of psychotic symptoms among regular methamphetamine users. DESIGN: Cross-sectional survey. SETTING: Participants were recruited from Sydney, Australia, through advertisements in free-press magazines, flyers and through word-of-mouth. PARTICIPANTS: Methamphetamine users (n = 309) who were aged 16 years or over and took the drug at least monthly during the past year. MEASUREMENTS: A structured face-to-face interview was used to assess drug use, demographics and symptoms of psychosis in the past year. Measures of psychosis included: (a) a psychosis screening instrument derived from the Composite International Diagnostic Interview; and (b) the Brief Psychiatric Rating Scale subscales of suspiciousness, unusual thought content, and hallucinations. Dependence on methamphetamine was measured using the Severity of Dependence Scale. FINDINGS: Thirteen per cent of participants screened positive for psychosis, and 23% had experienced a clinically significant symptom of suspiciousness, unusual thought content or hallucinations in the past year. Dependent methamphetamine users were three times more likely to have experienced psychotic symptoms than their non-dependent counterparts, even after adjusting for history of schizophrenia and other psychotic disorders. CONCLUSION: The prevalence of psychosis among the current sample of methamphetamine users was 11 times higher than among the general population in Australia. Dependent methamphetamine users are a particularly high-risk group for psychosis.