Almost half of the US states have adopted \medical marijuana” laws (MMLs),and 58% of Americans now favor marijuana legalization. Despite public support, federal law continues to prohibit the use and sale of marijuana due to public health concerns of increased abuse, drugged driving, and youth access. Using evidence from MMLs, this is the first paper to study whether growth in the size of legal marijuana markets affects illegal use and its associated health consequences. By collecting new data on per capita registered medical marijuana patient rates, I investigate how state supply regulations and changes in federal enforcement affect the size of this legal market. I then study how illegal marijuana use and other health outcomes respond to changes in legal availability. I find that growth in the legal medical marijuana market significantly increases recreational use among all age groups. Increased consumption among older adults has positive consequences in the form of an 11% reduction in alcohol- and opioid-poisoning deaths. However, increased consumption among youths leads to negative externalities. Raising the share of adults registered as medical marijuana patients by one percentage point increases the prevalence of recent marijuana use among adolescents and young adults by 5-6% and generates negative externalities in the form of increased traffic fatalities (7%) and alcohol poisoning deaths (4%).
Those results are consistent with my intuitions. When it comes to “those who already are screwed up,” namely the older generation, it is best to shunt them off into pot, compared to the relevant alternatives. But when it comes to the younger generation, the new norm that “pot is OK” may in fact not be best in the longer run. So in sum,while I (TC, not the author necessarily) favor marijuana decriminalization, we should hold mixed moods towards its practical effects.