A study challenges previous research that medical cannabis is associated with reduced opioid overdose deaths. Previous research has found reduced mortality rates from opioid overdose in US states with medical cannabis laws between 1999 and 2010. The finding has been cited as proof that medical cannabis legalization will prevent opioid overdose deaths, despite cautionary notes against drawing causal conclusions from ecological correlations. Chelsea Shover and colleagues used the methods in the earlier work to extend the available data through 2017. For the years 1999-2010, the authors found a 21% decrease in opioid overdose mortality associated with medical cannabis laws, in agreement with the earlier finding. However, when the data through 2017 were included in the analysis, the association between medical cannabis laws and overdose mortality changed from negative to positive, with implementation of a law associated with a 23% increase in mortality on average. The association remained positive even after controlling for different types of cannabis laws, and neither recreational nor low-THC cannabis laws were associated with changes in opioid overdose mortality. According to the authors, the observed associations between medical cannabis laws and opioid overdose mortality may be spurious, given that only around 2.5% of the US population uses medical cannabis.
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Article #19-03434: "Association between medical cannabis laws and opioid overdose mortality has reversed over time," by Chelsea L. Shover, Corey S. Davis, Sanford C. Gordon, and Keith Humphreys.
MEDIA CONTACT: Chelsea L. Shover, Stanford University, CA; tel: 650-721-6931, 717-283-6109; e-mail: <clshover@stanford.edu>
Journal
Proceedings of the National Academy of Sciences