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.