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Cannabis use is associated with mild, transient psychotic and affective experiences, but its long-term effects remain speculative. The U.K. government commissioned these authors to conduct a systematic review to address the question of whether cannabis use increases the risk for psychosis in later life. They now report a detailed review of seven cohort studies from the U.S., U.K., Europe, and New Zealand that met their criteria for handling of potential bias and confounding factors.
The risk for psychotic outcomes (defined as a range, with schizophrenia as the most severe manifestation) was higher in individuals who had ever used cannabis (adjusted odds ratio, 1.41) than in those who had not. A dose-response effect was observed, with increas…