Harvard Health Publications

Teens who smoke pot at risk for later schizophrenia, psychosis

Posted By Ann MacDonald On March 7, 2011

Teenagers and young adults who use marijuana may be messing with their heads in ways they don’t intend.

Evidence is mounting that regular marijuana use increases the chance that a teenager will develop psychosis, a pattern of unusual thoughts or perceptions, such as believing the television is transmitting secret messages. It also increases the risk of developing schizophrenia, a disabling brain disorder that not only causes psychosis, but also problems concentrating and loss of emotional expression.

In one recent study that followed nearly 2,000 teenagers as they became young adults, young people who smoked marijuana at least five times were twice as likely to have developed psychosis over the next 10 years as those who didn’t smoke pot.

Another new paper concluded that early marijuana use could actually hasten the onset of psychosis by three years. Those most at risk are youths who already have a mother, father, or sibling with schizophrenia or some other psychotic disorder.

Young people with a parent or sibling affected by psychosis have a roughly one in 10 chance of developing the condition themselves—even if they never smoke pot. Regular marijuana use, however, doubles their risk—to a one in five chance of becoming psychotic.

In comparison, youths in families unaffected by psychosis have a 7 in 1,000 chance of developing it. If they smoke pot regularly, the risk doubles, to 14 in 1,000.

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.)

While the research on marijuana and the mind has not yet connected all the dots, these new studies provide one more reason to caution young people against using marijuana—especially if they have a family member affected by schizophrenia or some other psychotic disorder. Although it may be a tough concept to explain to a teenager, the reward of a short-time high isn’t worth the long-term risk of psychosis or a disabling disorder like schizophrenia.

Related Information: Overcoming Addiction: Paths toward recovery

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