Interpreting Hazy Warnings About Pot and Mental Illness

By Paul Armentano
Smoking pot won't make you crazy, but trying to find the truth behind the recent rash of headlines regarding a supposed link between cannabis and mental illness might.

According to the Associated Press and other news sources, a new study in the British medical journal The Lancet reports that smoking cannabis - even occasionally - can increase one's risk of becoming psychotic. It sounds alarming at first, but a closer look at the evidence reveals that there's less here than the headlines imply.

First, there is no new study. The paper published in The Lancet is a meta-analysis -- a summary of seven studies that previously appeared in other journals, including some that were published decades ago. Second, the touted association between cannabis and mental illness is small--about the same size as the link between head injury and psychosis. Finally, despite what some new sources suggest, this association is hardly proof of a cause-and-effect relationship between cannabis and psychosis.

So why the sudden fuss?

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In fact, investigators actually reported that cannabis use was associated with a slight increase in psychotic outcomes. However, the authors emphasized (even if many in the media did not) that this small association does not reflect a causal relationship. Folks with psychoses use all intoxicants more often than other people do, including alcohol and tobacco.

Cannabis use can correlate with mental illness for many reasons. People often turn to cannabis to alleviate the symptoms of distress. A recent study performed in Germany showed that cannabis offsets certain cognitive declines in schizophrenic patients. Another study shows that psychotic symptoms predict later use of cannabis, suggesting that people might turn to the plant for help rather than become ill after use.

Perhaps the most impressive evidence against the cause-and-effect relationship concerns the unvarying rate of psychoses across different eras and different countries. People are no more likely to be psychotic in Canada or the United States (two nations where large percentages of citizens use cannabis) than they are in Sweden or Japan (where self-reported marijuana use is extremely low). Even after the enormous popularity of cannabis in the 1960s and 1970s, rates of psychotic disorders haven't increased.

Despite this evidence, we'd like to spread the word that cannabis is not for everybody. Teens should avoid the plant. Folks with a predisposition for mental illness should stay away, too. This potential for health risks in a few people, however, does not justify criminal prohibitions for everyone. (We wouldn't pass blanket prohibitions against alcohol simply to protect pregnant women, for example.) The underground market does an extremely poor job of keeping marijuana out of the hands of teens and others who should stay away from it. A regulated market could better educate users to potential risks and prohibit sales to young people.

Consequently, the review in The Lancet suggests that if cannabis really does alter risk for mental illness, we can't leave control of sales to folks who are willing to break the law. Instead, a taxed, regulated, age-restricted market is our best chance to keep any negative consequences of marijuana under control.

Paul Armentano is the senior policy analyst for NORML and the NORML foundation in Washington, DC. He resides in Pleasant Hill.

Mitch Earleywine is Associate Professor of Psychology at The University at Albany, State University of New York and author of "Understanding Marijuana" (Oxford University Press).