Its proponents argue that smoking marijuana makes you feel better. But according to a study published in the December issue of the American Journal of Psychiatry, adults who abuse the drug may be at greater risk for depression.

Gregory B. Bovasso of the University of Pennsylvania Treatment Research Center studied a random sample of 1,920 adults who were interviewed first in 1980 and again between 1994 and 1996. Subjects diagnosed with cannabis abuse at the start of the study were four times more likely to experience depressive symptoms, particularly suicidal thoughts and the inability to experience pleasure, than their non-smoking counterparts. Participants who were depressed at the outset of the study, however, were no more likely to abuse marijuana later on, the study found.

According to Bavasso, because the findings address new cases of depressive symptoms (instead of the prevalence of depression), they "underscore the importance of cannabis abuse prevention rather than treatment." Further research, he concludes, is needed to identify which characteristics of marijuana abusers account for their higher risk of depression.