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Medical cannabis laws appear no longer tied to drop in opioid overdose mortality

Correlations do not hold when analysis is expanded to 2017



Contrary to previous research indicating that medical cannabis laws reduced opioid overdose mortality, the association between these two has reversed, with opioid overdose mortality increased in states with comprehensive medical cannabis laws, according to Chelsea L. Shover, PhD, and associates.

medical marijuana Courtesy Wikimedia Commons/Coaster420/Creative Commons License

The original research by Marcus A. Bachhuber, MD, and associates showed that the introduction of state medical cannabis laws was associated with a 24.8% reduction in opioid overdose deaths per 100,000 population between 1999 and 2010. In contrast, the new research – which looked at a longer time period than the original research did – found that the association between state medical cannabis laws and opioid overdose mortality reversed direction, from ­–21% to +23%.

“We find it unlikely that medical cannabis – used by about 2.5% of the U.S. population – has exerted large conflicting effects on opioid overdose mortality,” wrote Dr. Shover, of the department of psychiatry and behavioral sciences at Stanford (Calif.) University, and associates. “A more plausible interpretation is that this association is spurious.” Their study was published in the Proceedings of the National Academy of Sciences.

To conduct their analysis, Dr. Shover and associates extended the timeline reviewed by Dr. Bachhuber and associates to 2017. During 2010-2017, 32 states enacted medical cannabis laws, including 17 allowing only medical cannabis with low levels of tetrahydrocannabinol (THC), and 8 legalized recreational marijuana. In the expanded timeline during 1999-2017, states possessing a comprehensive medical marijuana law saw an increase in opioid overdose mortality of 28.2%. Meanwhile, states with recreational marijuana laws saw a decrease of 14.7% in opioid overdose mortality, and states with low-THC medical cannabis laws saw a decrease of 7.1%. However, the investigators noted that those values had wide confidence intervals, which indicates “compatibility with large range of true associations.”

“The nonrobustness of the earlier findings also highlights the challenges of controlling scientific messages in controversial policy areas. Corporate actors with deep pockets have substantial ability to promote congenial results, and suffering people are desperate for effective solutions. Cannabinoids have demonstrated therapeutic benefits, but reducing population-level opioid overdose mortality does not appear to be among them,” Dr. Shover and associates noted.

Dr. Shover reported receiving support from National Institute on Drug Abuse and the Wu Tsai Neurosciences Institute. Another coauthor received support from the Veterans Health Administration, Wu Tsai Neurosciences Institute, and the Esther Ting Memorial Professorship at Stanford.

SOURCE: Shover CL et al. Proc Natl Acad Sci U S A. 2019 Jun 10. doi: 10.1073/pnas.1903434116.

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