Reefer Madness

Researchers find evidence of relationship between marijuana use and onset of psychotic illnesses

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Psychotic illnesses may develop earlier in those who smoke marijuana compared to those who do not smoke the plant.

According to a recent analysis of 83 previously published studies, psychotic illnesses developed 2.7 years sooner in patients who smoke marijuana than in patients who had not. The Australian researchers who conducted the analysis also looked at the relationship between the use of other psychoactive substances (such as alcohol) and the age of onset of psychosis. In contrast to their findings on marijuana, alcohol use alone did not appear to affect an earlier onset of psychosis.

Looking at existing hypotheses on the relationship between marijuana and schizophrenia, the study's authors believe their findings support the idea that smoking marijuana triggers psychosis in at-risk individuals. However, that hypothesis is a point of contention. Another popular explanation posits that people who are vulnerable to psychosis naturally gravitate toward substances such as marijuana.

Nonetheless, the authors of this meta-analysis write that their findings "do not support the view that people with a propensity to develop psychosis at a young age are simply more likely to use all substances, because alcohol use was not associated with [an earlier onset of psychosis]."

They conclude by writing that their results offer strong evidence that many cases of psychotic illness could be delayed, or even prevented, if we reduce the use of marijuana among young people. If marijuana use is related to the early onset of psychosis, the authors argue that reducing the use of marijuana could allow patients to reach important developmental milestones of late adolescence and early adulthood. Reaching that point before psychosis sets in might help patients avoid the long-term disabilities that are caused by psychotic illnesses.

According to the National Institute on Drug Abuse, 11.8 percent of 8th-graders reported using marijuana in the past year; 26.7 percent of 10th-graders reported past-year use; and 32.9 percent of 12th-graders reported using marijuana within the last year.

The Australian study is published the Archives of General Psychiatry.

Reviewed by: 
Review Date: 
February 8, 2011
Last Updated:
February 11, 2011