Think smoking marijuana is harmless? Think again. Chronic users of the drug often find themselves lacking motivation. Some even seem depressed or have other signs of mental illness. But does chronic marijuana use lead to psychiatric problems? Or do people suffering from mental illness use marijuana to self-medicate? While this drug was becoming increasingly popular with young people in the 1990s, researchers were busy trying to figure out if marijuana was a cause or an effect of psychiatric problems. And their work seems to have paid off. Research now indicates that marijuana use increases the risk of depression, as well as schizophrenia. But at the same time, depressed people do not use marijuana more often than their non-depressed counterparts.

In an Australian study, researchers interviewed 1,600 14- and 15-year-olds, then again seven years later. Participants filled out a questionnaire, reporting on their use of marijuana and symptoms of depression or anxiety. A surprising 60% of the participants had used marijuana by the time they were 20. The researchers found that the young women who had used marijuana weekly as teenagers were twice as likely to have depression as a young adult than women who did not use the drug. Daily use as a teenager was associated with four times the risk of depression for young women.

Also, among the young adults, women who used marijuana daily were five times more likely to experience depression and anxiety than those who did not use the drug. However, the researchers found no relationship between teenage depression and anxiety and later use of marijuana. This refutes the idea that youths suffering from depression turn to marijuana as a way of self-medicating.

Another study involved close to 2,000 participants in the Baltimore area who were interviewed in 1980 and then again between 1994 and 1996. The researchers assessed the participants for signs of marijuana abuse and symptoms of depression. Researchers defined abusers of marijuana as people for whom the drug caused social problems, such as inability to perform at work. The results showed people who initially did not have depressive symptoms but abused marijuana were more than four times as likely to have depressive symptoms at the follow-up date than those who did not abuse marijuana. The depressive symptoms associated with earlier marijuana abuse included suicidal thoughts and a feeling of boredom. As in the Australian study, participants with depressive symptoms at the start of the study were not more likely to abuse marijuana later on than participants without such symptoms.

Marijuana use has also been linked to schizophrenia. In a study of 50,000 Swedish military draftees, the use of marijuana during adolescence was associated with a 30% increase in risk of developing schizophrenia. The study also showed a higher risk of schizophrenia with more frequent marijuana use. The researchers of this study found these results were independent of personality traits and the use of other drugs.

From these studies, it is clear that marijuana use is related to subsequent depression and schizophrenia. It is still not clear, however, whether marijuana triggers the onset of illness in individuals predisposed to such conditions or whether it actually causes the illnesses. Some researchers believe that psychosocial factors that result from marijuana use—such as educational failure and unemployment—may contribute to depression. Other researchers think that marijuana may have a lasting chemical effect on the central nervous system and its functions involving memory, emotion, cognition, and movement.

In addition to its widespread availability, marijuana’s recent popularity may be largely based on the perception that it is safer than cigarettes and alcohol, according to an editorial in the British Medical Journal. But these studies show marijuana is not the harmless drug many believe it is, but that it can have a negative impact on your mental health.

Sources: British Medical Journal, November 2002 and American Journal of Psychiatry December 2001

May 2003 Update

http://www.health.harvard.edu/fhg/updates/update0503c.shtml