Many studies have linked marijuana use with early onset of psychosis. The question is, does smoking marijuana cause earlier psychosis? A new review of 83 studies involving more than 22,000 participants seeks an answer.
The meta-analysis found that people who smoked marijuana developed psychotic disorders an average 2.7 years earlier than people who did not use cannabis. But the review also found that people who used any illegal drug suffered psychosis two years earlier than non-users, not a large difference.
While alcohol use was not associated with early onset, the studies reviewed could not rule out the influence of cigarette smoking, which is a common habit of people with psychotic disorders and those who smoke marijuana. In many of the countries from which the data was gathered, in fact, cannabis is typically smoked mixed with tobacco. The researchers argue that cigarette smoking—unlike marijuana— does not worsen hallucinations or paranoia in patients with schizophrenia, so they believe that tobacco does not account for earlier onset.