The article discusses a review to determine if cannabis causes chronic psychotic or affective symptoms other than temporary intoxication. Longitudinal population-based studies with psychotic outcomes such as schizophrenia, delusions, and hallucinations were examined. Similar studies were grouped in a meta-analysis using the DerSimonian and Laird random-effects model. The results indicated a greater chance of psychotic effects in individuals who used cannabis, with risk increasing with frequent cannabis use.