Effect of Cannabis on Mortality

"In summary, this study showed little, if any, effect of marijuana use on non-AIDS mortality in men and on total mortality in women. The increased risk of AIDS mortality in male marijuana users probably did not reflect a causal relationship, but most likely represented uncontrolled confounding by male homosexual behavior. The risk of mortality associated with marijuana use was lower than that associated with tobacco cigarette smoking."

Source: 

Stephen Sidney, MD, Jerome E. Beck, DrPH, Irene S. Tekawa, MA, Charles P Quesenberry, Jr, PhD, and Gary D. Friedman, MD, “Marijuana Use and Mortality.” American Journal of Public Health 87.4 (1997) pp. 589–590.