Have a look at this study published from the American Public Health Association! Here the abstract:
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.
Read full study: http://ajph.aphapublications.org/doi/abs/10.2105/AJPH.2013.301612