By Pat Anson, Editor

The availability of medical marijuana has significantly reduced opioid prescribing for Medicaid and Medicare patients, according to two large studies published in the Journal of the American Medical Association (JAMA).

In one study, researchers at the University of Georgia looked at Medicare Part D prescription drug data from 2010 to 2015. They found that the number of daily doses prescribed for morphine (-14%), hydrocodone (-10.5%) and fentanyl (-8.5%) declined in states with medical marijuana laws. However, daily doses for oxycodone increased (+4.4%) in those same states.

The drop in opioid prescribing was most pronounced in states that have medical marijuana dispensaries, as opposed to those that only allow home cultivation of cannabis for medical purposes.

“We found that prescriptions for hydrocodone and morphine had statistically significant negative associations with medical cannabis access via dispensaries,” wrote lead author W. David Bradford, PhD, Department of Public Administration and Policy at the University of Georgia.

“Combined with previously published studies suggesting cannabis laws are associated with lower opioid mortality, these findings further strengthen arguments in favor of considering medical applications of cannabis as one tool in the policy arsenal that can be used to diminish the harm of prescription opioids.”

The second study, by researchers at the University of Kentucky, looked at Medicaid prescriptions from 2011 to 2016, and found a 5.88% decline in opioid prescribing in states with medical marijuana laws.  Opioid prescribing for Medicaid patients fell even more -- by 6.38% -- in states where the recreational use of marijuana is legal.

“These findings suggest that medical and adult-use marijuana laws have the potential to reduce opioid prescribing for Medicaid enrollees, a segment of population with disproportionately high risk for chronic pain, opioid use disorder, and opioid overdose,” wrote lead author Hefei Wen, PhD, University of Kentucky College of Public Health.

One weakness of both studies is that they did not determine if Medicaid and Medicare patients reduced their use of opioid medication because they were using cannabis.  They also only included patients that were elderly, poor or disabled. And they were conducted during a period when nationwide opioid prescribing was in decline.

A recent study by the RAND corporation found little evidence that states with medical marijuana laws experience reductions in the volume of legally prescribed opioid medication. RAND researchers believe some pain patients may be experimenting with marijuana, but their numbers are not large enough to have a significant impact on prescribing. 

"If anything, states that adopt medical marijuana laws... experience a relative increase in the legal distribution of prescription opioids," the RAND study found. "Either the patients are continuing to use their opioid pain medications in addition to marijuana, or this patient group represents a small share of the overall medical opioid using population." 

Although 29 states and the District of Columbia have legalized medical marijuana and a handful of states allow its recreational use, marijuana remains illegal under federal law.