States that have approved medical cannabis laws saw a dramatic reduction in opioid use, according to a new study by researchers at the University of Georgia.

In a paper published today in the Journal of the American Medical Association, Internal Medicine, researchers examined the number of all opioid prescriptions filled between 2010 and 2015 under Medicare Part D, the prescription drug benefit plan available to Medicare enrollees.

In states with medical cannabis dispensaries, the researchers observed a 14.4 percent reduction in use of prescription opioids and nearly a 7 percent reduction in opiate prescriptions filled in states with home-cultivation-only medical cannabis laws.

"Some of the states we analyzed had medical cannabis laws throughout the five-year study period, some never had medical cannabis, and some enacted medical cannabis laws during those five years," said W. David Bradford, study co-author and Busbee Chair in Public Policy in the UGA School of Public and International Affairs. "So, what we were able to do is ask what happens to physician behavior in terms of their opiate prescribing if and when medical cannabis becomes available."

Since California approved the first medical cannabis law in 1996, 29 states and the District of Colombia have approved some form of medical cannabis law.

"Physicians cannot prescribe cannabis; it is still a Schedule I drug," Bradford said. "We're not observing that prescriptions for cannabis go up and prescriptions for opioids go down. We're just observing what changes when medical cannabis laws are enacted, and we see big reductions in opiate use."

The researchers examined all common prescriptions opiates, including hydrocodone, oxycodone, morphine, methadone and fentanyl. Because heroin is not a legal drug, it was not included as part of the study.

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Last year, the U.S. Department of Health and Human Services declared a public health emergency related to the abuse of opiates. Opioid overdoses accounted for more than 42,000 deaths in 2016, more than any previous year on record, and more than 40 percent of opioid overdose deaths involved a prescription opioid, according to HHS.

Opioid prescription rates increased from about 148 million prescriptions in 2005 to 206 million prescriptions by 2011, Bradford said. This coincided with an increase in the number of opioid-related deaths.

"There is a growing body of literature that suggests cannabis may be used to manage pain in some patients, and this could be a major component of the reductions we see in the use of opiates," he said.

The researchers did not, however, see any significant reductions in the number of non-opioid drugs prescribed during the study period.

"In other studies, we examined prescription rates for non-opioid drugs such as blood thinners, flu medications and phosphorus stimulants, and we saw no change," said Ashley Bradford, lead author of the study and graduate student in UGA's department of public administration and policy. "Medical cannabis wouldn't be an effective treatment for flu or for anemia, so we feel pretty confident that the changes we see in opioids are because of cannabis because there is a legitimate medical use."

The researches concede that if medical cannabis is to become an effective treatment, there is still much work to be done. Scientists are only just beginning to understand the effects of the compounds contained in cannabis, and an effective "dose" of cannabis would need to be defined clearly so that each patient receives a consistent dose.

"Regardless, our findings suggest quite clearly that medical cannabis could be one useful tool in the policy arsenal that can be used to diminish the harm of prescription opioids, and that's worthy of serious consideration," David Bradford said.

Coauthors on the paper Amanda Abraham, assistant professor of public administration and policy at UGA and Grace Bagwell Adams, assistant professor of health policy and management in UGA's College of Public Health.