Cannabis use and misuse prevalence among people with psychosis.

BACKGROUND Increasing attention has been given by researchers to cannabis use in individuals with psychosis. As psychoses are relatively low-prevalence disorders, research has been mostly been restricted to small-scale studies of treatment samples. The reported prevalence estimates obtained from these studies vary widely. AIMS To provide prevalence estimates based on larger samples and to examine sources of variability in prevalence estimates across studies. METHOD Data from 53 studies of treatment samples and 5 epidemiological studies were analysed. RESULTS Based on treatment sample data, prevalence estimates were calculated for current use (23.0%), current misuse (11.3%), 12-month use (29.2%), 12-month misuse (18.8%), lifetime use (42.1%) and lifetime misuse (22.5%). Epidemiological studies consistently reported higher cannabis use and misuse prevalence in people with psychosis. CONCLUSIONS The factor most consistently associated with increased odds of cannabis prevalence was specificity of diagnosis. Factors such as consumption patterns and study design merit further consideration.