Medical Marijuana Laws and Suicide

Abstract

In the current study we use a synthetic control group design 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.” Utilizing a panel dataset containing annual frequencies of Total, gun, and non-gun suicides aggregated by state for the years 1970–2004, we construct a control time series for California as a weighted combination of the 41 states that did not legalize marijuana during the analysis period. Post-intervention differences for California and its constructed control time series can be interpreted as the effects of the medical marijuana law on suicide. Significance of the effects were assessed with permutation tests. Our findings suggest that California’s 1996 legalization resulted in statistically significant (p<.05) reductions in suicides and gun suicides, but only a non-significant reduction in non-gun suicides (p≥.488). 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 that the effect on total suicide is driven by gun suicide alone.

Keywords:

• medical marijuana
• suicide risk
• synthetic control design
• firearms

Notes

1 In 2011, a Nevada medical user attempted to purchase a firearm and was refused. Claiming a violation of Second Amendment rights, the user sued. A trial court dismissed the suit and in 2016, the dismissal was affirmed by an appeals court. Wilson v. Lynch et al., U.S. Court of Appeals for the Ninth Circuit, No. 14-15700.

2 The ICD 8 protocol does not distinguish between firearms and explosives.

3 Prior to the ICD-8a revision adopted in 1968, physicians did not report whether external causes of death were intentionally self-inflicted, accidental, or malicious. Under the ICD-7, a firearm suicide would have been coded as a general explosive fatality, with no indication of intentional self-harm, accidental injury, or intentional suicide (Gjertsen, 2015).

Additional information

Notes on contributors

Bradley J. Bartos

Bradley J. Bartos, Criminology, Law and Society, University of California, Irvine, CA, USA.

Charis E. Kubrin

Charis E. Kubrin, Criminology, Law and Society, University of California, Irvine, CA, USA.

Carol Newark

Carol Newark, Criminology, Law and Society, University of California, Irvine, CA, USA.

Richard McCleary

Richard McCleary, Criminology, Law and Society, University of California, Irvine, CA, USA.