Evidence of the association between cannabis and depression was obtained through a search of Medline, Psychinfo, and EMBASE databases to obtain information on relevant research. Cohort studies and well-designed cross-sectional studies in the general population found a modest association between heavy or problematic cannabis use and depression. There was little evidence of an association between depression and infrequent cannabis use. A number of studies also found a modest association between early-onset, regular cannabis use and depression later in life, which persisted after controlling for potential confounding variables. Given little evidence of an increased risk for later cannabis use among people with depression, there was weak support for the self-medication hypothesis for the link between depression and cannabis use. A limited number of studies have controlled for potential confounding variables in an analysis of the association between heavy cannabis use and depression. Such studies found that the risk is significantly reduced by statistical control; however, a modest relationship remains. Although this review did find a link between heavy cannabis use and symptoms of depression, the authors conclude that it is too early in the research to discount the hypothesis that this association may be due to common social, family, and contextual factors that increase the risks for both heavy cannabis use and depression, without there being a link between the two. Suggestions are offered for research in this area. 98 references