Medical Marijuana Laws and Suicide

Abstract

Objective: To estimate the causal effect of a medical marijuana initiative on suicide risk. In 1996, California legalized marijuana use for medical purposes. Implementation was abrupt and uniform, presenting a “natural experiment.”

Method: Total, gun and non-gun suicides were aggregated by state for the years 1970-2004. California’s control time series was constructed as a weighted combination of the 41 states that did not legalize marijuana during the time-frame. Post-intervention differences for California and its constructed control time-series were interpreted as the effects of the medical marijuana law on suicide. Significance of the effects were assessed with permutation tests.

Results: The 1996 legalization resulted in mean annual reductions of 398.9 total suicides, 208 gun suicides, and 135 non-gun suicides. The effect estimates for total and gun suicides were statistically significant (p<.05) but the effect estimate for non-gun suicides was not (p≥.488).

Conclusions: Since the effect for non-gun suicides was indistinguishable from chance, we infer that the overall causal effect was realized through gun suicides. The mechanism could not be determined, however. Participation in the medical marijuana program legally disqualifies participants from purchasing guns. But since most suicides involve guns, it is possible the effect on total suicide is driven by gun suicide alone.

Keywords: medical marijuana, suicide risk, synthetic control design, firearms