Harvard Mental Health Letter

In Brief: Study strengthens evidence that early marijuana use increases risk of psychosis

Several studies strongly suggest that using marijuana — particularly in the teenage years — can increase risk of developing psychosis. Now an analysis not only adds to this evidence, but also suggests that use of marijuana and other drugs at a young age may hasten the onset of psychosis.

Australian researchers analyzed studies that compared rates of psychosis in patients who previously used marijuana, other drugs, and alcohol with those who did not. They restricted their search to studies that included age of onset of first psychotic episode. They identified 83 studies enrolling more than 8,000 patients who used marijuana, other drugs, or alcohol and compared psychosis outcomes with 14,000 patients who did not.

They found that a first episode of psychosis occurred nearly three years earlier in people who used marijuana — and two years earlier in people who used an unspecified type of drug — than in people who did not. Use of alcohol did not affect age of onset of psychosis.

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