Prescriptions for opioid painkillers for chronic pain have increased in the United States and so have overdose deaths, but a new study focused on how the availability of alternative nonopioid treatment, such as medical marijuana, may affect overdose rates. 

States that implemented medical marijuana laws appear to have lower annual opioid analgesic overdoses death rates (both from prescription pain killers and illicit drugs such as heroin) than states without such laws although the reason why is not clear.

The authors examined the implementation of state medical marijuana laws and opioid analgesic overdose deaths in the United States between 1999 and 2010. Three states had medical marijuana laws prior to 1999, 10 states implemented laws between 1999 and 2010 and nine states had laws that went into effect after 2010, which was beyond the study period. The authors also considered New Jersey's law effective after the study period because it took effect in the last quarter of 2010. The authors analyzed state laws and death-certificate data.  

States with medical marijuana laws had a 24.8 percent lower average annual opioid overdose death rate compared to states without such laws. In 2010, that translated to about 1,729 fewer deaths than expected. The years after implementation of medical marijuana laws also were associated with lower overdose death rates that generally got stronger over time: year 1 (-19.9 percent), year 2 (-25.2 percent), year 3 (-23.6 percent), year 4 (-20.2 percent), year 5 (-33.7 percent) and year 6 (-33.3 percent).

Discussion: "In summary, although we found a lower mean annual rate of opioid analgesic mortality in states with medical cannabis laws, a direct causal link cannot be established. … If the relationship between medical cannabis laws and opioid analgesic overdose mortality is substantiated in further work, enactment of laws to allow for use of medical cannabis may be advocated as part of a comprehensive package of policies to reduce the population risk of opioid analgesics," write Marcus A. Bachhuber, M.D., of the Philadelphia Veterans Affairs Medical Center, and colleagues. 

Citation: JAMA Intern Med. doi:10.1001/jamainternmed.2014.4005. 

Commentary: Legalization of Medical Marijuana and Incidence of Opioid Mortality

In a related commentary, Marie J. Hayes, Ph.D., of the University of Maine, Orno, and Mark S. Brown, M.D., of the Eastern Maine Medical Center, Bangor, write: "If medical marijuana laws afford a protective effect, it is not clear why. If the decline in opioid analgesic-related overdose deaths is explained, as claimed by the authors, by increased access to medical marijuana as an adjuvant medication for patients taking prescription opioids, does this mean that marijuana provides improved pain control that decreases opioid dosing to safer levels?"

"The potential protective role of medical marijuana in opioid analgesic-associated mortality and its implication for public policy is a fruitful area for future work," they conclude.

JAMA Intern Med. doi:10.1001/jamainternmed.2014.2716.