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Marijuana evokes psychotic-like symptoms in susceptible individuals (see JW Psychiatry Mar 14 2011), and cannabis use may be associated with an earlier age of onset of psychotic illness. But does marijuana cause psychosis, or are the people who are destined to become psychotic more likely to use the drug? With more than 16 million regular pot smokers in the U.S., the question is important. This meta-analysis of 83 studies of the age at onset of psychosis involved 8167 psychosis patients who used psychoactive substances and 14,352 nonusing psychosis patients.
The results confirmed that the age at onset of psychosis was almost 3 years earlier in cannabis users than in nonusers. Alcohol use was not significantly associated with earlier onset of…