摘要：Objectives. We estimated the association between legalizing medical marijuana and suicides. Methods. We obtained state-level suicide data from the National Vital Statistics System’s Mortality Detail Files for 1990–2007. We used regression analysis to examine the association between medical marijuana legalization and suicides per 100 000 population. Results. After adjustment for economic conditions, state policies, and state-specific linear time trends, the association between legalizing medical marijuana and suicides was not statistically significant at the .05 level. However, legalization was associated with a 10.8% (95% confidence interval [CI] = −17.1%, −3.7%) and 9.4% (95% CI = −16.1%, −2.4%) reduction in the suicide rate of men aged 20 through 29 years and 30 through 39 years, respectively. Estimates for females were less precise and sensitive to model specification. Conclusions. Suicides among men aged 20 through 39 years fell after medical marijuana legalization compared with those in states that did not legalize. The negative relationship between legalization and suicides among young men is consistent with the hypothesis that marijuana can be used to cope with stressful life events. However, this relationship may be explained by alcohol consumption. The mechanism through which legalizing medical marijuana reduces suicides among young men remains a topic for future study. Although marijuana remains illegal under federal law, 21 states and the District of Columbia have legalized its use for medicinal purposes, and more than a dozen state legislatures have recently considered medical marijuana bills. There is evidence that the use of marijuana is associated with depression, suicidal ideation, and suicide attempts, 1–3 but no previous study has examined the association between legalizing medical marijuana and completed suicides, the 10th leading cause of death in the United States. 4 Medical marijuana laws remove criminal penalties for using, possessing, and cultivating marijuana for medicinal purposes. In addition, medical marijuana laws provide doctors immunity from prosecution for recommending the use of marijuana to their patients. Because it is prohibitively expensive for the government to ensure that all marijuana ostensibly grown for the medicinal market ends up in the hands of registered patients, diversion to the recreational market almost certainly occurs. Indeed, the legalization of medical marijuana is associated with a 10% to 26% decrease in the price of high-quality marijuana. 5 It is also associated with increased use of marijuana by young adults accompanied by substantial reductions in alcohol consumption and binge drinking. 5,6 Animal studies show that, at low doses, synthetic cannabinoid injections can have a potent antidepressant effect, 7,8 and higher dosages reduce serotonin transmission and lead to depression-like behavior. 8,9 Epidemiological studies provide evidence that marijuana use is associated with the symptoms of depression and suicidal ideation. 10,11 However, any association between marijuana use and outcomes such as these could be attributable to difficult-to-measure confounders at the individual level (e.g., personality) or reflect reverse causality stemming from self-medication. 10,12,13 Using state-level data and an empirical approach designed to account for the influence of difficult-to-measure confounders and reverse causality, we examined the association between legalizing medical marijuana and year-to-year changes in the suicide rate. In addition, because males respond to cannabinoids differently than females, 14–16 and because there are distinct age patterns to substance use, 17 we examined the association between legalizing medical marijuana and suicides by gender and age.
