The Impact of Statewide Legalization of Marijuana on Opioid Overdoses

It has been speculated for decades that the use of more mild drugs such as marijuana leads to the use of harder drugs like opioids, a theory known as the Gateway Hypothesis. This hypothesis informed many policy changes in the last half century, but there has been a recent shift towards statewide legalization of marijuana. This paper analyzes the impact of the legalization of marijuana, both medically and recreationally, on the opioid overdose death rate using the synthetic control method, which will indicate the validity of the Gateway Hypothesis. This paper, when using a conventional fixed effects model, finds that medical legalization of marijuana causes an increase in opioid deaths, and the coefficient on recreational legalization is also positive but smaller and not statistically significant. However, recreational legalization appears to have heterogeneous effects on opioid deaths, which is captured by the synthetic controls method. By contrast, the synthetic controls method shows a more consistent increase in opioid deaths across states when marijuana is legalized for medical use