Does Long-Term Cannabis Use Increase Risk for Psychosis?

Few data are available on the long-term effects of cannabis use on the development of mental illness. Researchers reviewed data from population-based studies that examined cannabis use and later development of psychotic or affective symptoms or disorders.

In pooled analysis of data from seven cohort studies adjusted for confounding, the risk for any psychotic outcome in people who had ever used cannabis was increased by 41% compared with nonusers. Pooled analysis of results from six studies showed evidence of a dose-response effect; the most frequent users had twice the risk for later psychotic outcomes compared with nonusers. One of two studies that examined the effect of age at first use reported a greater effect among those who first used…