States with medical marijuana laws have fewer deaths from opioid overdoses compared to states that do not allow medical marijuana, according to new research.

Opioids for chronic pain, like OxyContin, Percocet and Vicodin, are meant to suppress pain. Recent data shows that not only are prescriptions for these drugs up, but rates of overdose and death are increasing as well. New research published Monday in the journal JAMA Internal Medicine shows that states with medical marijuana laws have rates of anticipated opioid-related deaths 25% lower than states that don’t allow it.

The researchers looked at death rates from opioids between 1999 and 2010 and found that the 13 states that allowed medical marijuana at the time had lower opioid mortality rates–the hypothesis being that patients with chronic pain perhaps switched from the heavy drugs to marijuana, since cannabinoids in marijuana react similarly in the brain. About 60% of all opioid deaths happen among people who have legitimate prescriptions, but abuse is also problematic. “Among people who use opioids illicitly, a relatively high proportion of them also use marijuana,” says study author Dr. Marcus Bachhuber of the Philadelphia VA Medical Center.

Though the findings are intriguing, the researchers could not prove causation, and there are many possible explanations for the findings. States with medical marijuana laws may also have implemented more rules regarding opioid prescriptions or offered more education to doctors and patients about their addictive qualities. And several states like Minnesota and New York have passed at least limited legalized medical marijuana since 2010, so the findings already need to be updated. Still, if there is in fact an association, Bachhuber believes it’s encouraging. “I think that any change that leads to fewer people dying of opioid overdoses would be a positive.”

The researchers say more research is needed to understand why people choose medical marijuana and whether people at risk for opioid abuse would consider it as an alternative. There’s also the issue of presenting a split medical community with the risks and benefits of prescribing someone marijuana.

“I know many doctors struggle with the issue of who would be best to treat medical marijuana. There are some doctors who say that there is no valid medical use,” says Bachhuber. “I think that leaves a tremendous opportunity for future studies to help guide use to look at the risk and benefits and in clinical practice.”

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