Association between medical cannabis laws and opioid overdose mortality has reversed over time. Chelsea L. Shover et al. PNAS. 2019. Article

Lena Yannella

 

The Problem: In 2014, Bachhuber et al. published a study revealing a correlation between state legalization of medical cannabis and a reduction in deaths by opioid overdose between 1999 and 2010. This finding generated widespread media attention, prompting the conclusion that expanding the use of medical cannabis could reverse or diminish the opioid epidemic.

 

Why do this study? Although Bachhuber et al.’s early study was promising, the opioid crisis has intensified since 2010, the last year of data they analyzed, despite the legalization of marijuana for medical or recreational purposes in some states. It’s important to understand whether cannabis has continued to suggest reductions in opioid deaths since then.

 

The study: This study replicated the methods of Bachhuber et al., generating a generalized linear model to compare opioid overdose deaths with the implementation of medical cannabis laws. Within the time period of 1999 until 2010, the results matched those of Bachhuber et al., with a 21.1% decrease in deaths per 100,000 population associated with the enactment of a medical cannabis law. However, in subsequent years, the current study found that the impact decreased in magnitude. And between 1999 and 2017, the final year of this study sample, the introduction of a medical cannabis law was associated with a 22.7% increase in deaths by overdose per 100,000 population.

 

Conclusions: This study calls into question the conventional wisdom that greater access to cannabis is associated with fewer deaths by opioid overdose. That may have been true early in the trajectory of cannabis legalization, but it does not seem to be the case since 2010. More ­broadly, especially in the absence of a clear explanation for why results should be different pre- and post-2010, this study raises the question of whether the observed reduction in opioid deaths that accompanies cannabis legalization is really due to cannabis laws, or whether it is due to other social, legal, and economic variables.

 

Funder: None

 

Author conflicts: None

 

Commentary (David Casarett MD): This study is bound to cause some controversy. Also some disappointment. Many of us in the field have been optimistic that cannabis could help reduce the impact and severity of the opioid epidemic, and Marcus Bachhuber’s 2012 study was very encouraging. Now this study supports those earlier results, but only between 1999 and 2010. From then until 2017, the association between cannabis legalization and opioid deaths goes to zero and then heads in the other direction. What do we believe? Right now, it seems possible that cannabis may not reduce opioid deaths at the population level, and that some or all of the changes in opioid deaths we see in studies like these are due to other factors such as availability of naloxone for first responders, or high-quality addiction treatment programs. Nevertheless, there is growing evidence that cannabis can help patients reduce the use of other medications, so future research should begin there: following patients over time to see whether cannabis use helps reduce opioid use and, in turn, whether it contributes to reductions in mortality.