[Dion]

For years, now, experts have been sounding the alarm about a possible link between marijuana use and psychosis. One of the best-known studies followed nearly 50,000 young Swedish soldiers for 15 years. Those who had smoked marijuana at least once were more than twice as likely to develop schizophrenia as those who had never smoked pot. The heaviest users (who said they used marijuana more than 50 times) were six times as likely to develop schizophrenia as the nonsmokers.

So far, this research shows only an association between smoking pot and developing psychosis or schizophrenia later on. That’s not the same thing as saying that marijuana causes psychosis.

This is how research works. Years ago, scientists first noted an association between cigarette smoking and lung cancer. Only later were they able to figure out exactly how cigarette smoke damaged the lungs and other parts of the body, causing cancer and other diseases.

The research on marijuana and the brain is at a much earlier stage. We do know that THC, one of the active compounds in marijuana, stimulates the brain and triggers other chemical reactions that contribute to the drug’s psychological and physical effects.

But it’s not clear how marijuana use might lead to psychosis. One theory is that marijuana may interfere with normal brain development during the teenage years and young adulthood.

The teenage brain is still a work in progress. Between the teen years and the mid-20s, areas of the brain responsible for judgment and problem solving are still making connections with the emotional centers of the brain. Smoking marijuana may derail this process and so increase a young person’s vulnerability to psychotic thinking. (You can read more about how the adolescent brain develops in this article from the Harvard Mental Health Letter.)

http://www.health.harvard.edu/blog/t...s-201103071676