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Are Smoking Pot and Psychosis Linked?

Marijuana Boosts Later Psychotic Illness Risk by 40%, Study Shows

Perspective on Marijuana and Mental Health

"The article is worth paying attention to," Bruce Spring, MD, an assistant professor of clinical psychiatry at the University of Southern California Keck School of Medicine, Los Angeles, an expert familiar with the study but not involved in it.

"It certainly gives cause for concern," Spring says of the findings about marijuana and psychosis risks. Still, he says, the overall risk is relatively low, statistically speaking.

"In general, the overall risk of someone getting a psychotic illness is about 3%," he says. "Now what this study is saying is that that 3% risk is increased by 40% [or more]," he says. So the risk with marijuana use would rise to 4.2%.

Put another way: In a group of 100 people, three would be expected, statistically speaking, to develop a psychotic illness such as schizophrenia or bipolar disorder with psychosis. "When you factor in the marijuana study, one or two more, depending on how often they use it, will have psychotic illness," Spring says.

Advice From the Experts

Says Spring, "I would tell people there is now some pretty good evidence that smoking marijuana can have some harmful consequences, and they are putting their future well-being at risk [if they smoke marijuana]. The more you smoke, the greater the risk, according to this study."

Zammit, the study co-author, adds, "I think the important message is to be aware of these risks." Those who have other risk factors for psychotic illness, such as a family history, might want to pay closer attention, he tells WebMD.

The research was funded by the U.K. Department of Health. Two co-authors were invited experts on the government’s Advisory Council on the Misuse of Drugs Cannabis Review in 2005; some co-authors received research money or other fees from pharmaceutical companies, including consultation on antipsychotic medication.

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