NEW YORK (Reuters Health) – Researchers aren’t sure why, but in the 23 U.S. states where medical marijuana has been legalized, deaths from opioid overdoses have decreased by almost 25 percent, according to a new analysis.

“Most of the discussion on medical marijuana has been about its effect on individuals in terms of reducing pain or other symptoms,” said lead author Dr. Marcus Bachhuber in an email to Reuters Health. “The unique contribution of our study is the finding that medical marijuana laws and policies may have a broader impact on public health.”

California, Oregon and Washington first legalized medical marijuana before 1999, with 10 more following suit between then and 2010, the time period of the analysis. Another 10 states and Washington, D.C. adopted similar laws since 2010.

For the study, Bachhuber, of the Philadelphia Veterans Affairs Medical Center and the University of Pennsylvania, and his colleagues used state-level death certificate data for all 50 states between 1999 and 2010.

In states with a medical marijuana law, overdose deaths from opioids like morphine, oxycodone and heroin decreased by an average of 20 percent after one year, 25 percent by two years and up to 33 percent by years five and six compared to what would have been expected, according to results in JAMA Internal Medicine.

Meanwhile, opioid overdose deaths across the country increased dramatically, from 4,030 in 1999 to 16,651 in 2010, according to the Centers for Disease Control and Prevention (CDC). Three of every four of those deaths involved prescription pain medications.

Of those who die from prescription opioid overdoses, 60 percent have a legitimate prescription from a single doctor, the CDC also reports.

Medical marijuana, where legal, is most often approved for treating pain conditions, making it an option in addition to or instead of prescription painkillers, Bachhuber and his coauthors wrote.

In Colorado, where recreational growth, possession and consumption of pot has been legal since 2012 and a buzzing industry for the first half of 2014, use among teens seems not to have increased (see Reuters story of July 29, 2014 here: reut.rs/1o040NI).

Medical marijuana laws seem to be linked with higher rates of marijuana use among adults, Bachhuber said, but results are mixed for teens.

But the full scope of risks, and benefits, of medical marijuana is still unknown, he said.

“I think medical providers struggle in figuring out what conditions medical marijuana could be used for, who would benefit from it, how effective it is and who might have side effects; some doctors would even say there is no scientifically proven, valid, medical use of marijuana,” Bachhuber said. “More studies about the risks and benefits of medical marijuana are needed to help guide us in clinical practice.”

Marie J. Hayes of the University of Maine in Orno co-wrote an accompanying commentary in the journal.

“Generally healthcare providers feel very strongly that medical marijuana may not be the way to go,” she told Reuters Health. “There is the risk of smoke, the worry about whether that is carcinogenic but people so far haven’t been able to prove that.”

There may be a risk that legal medical marijuana will make the drug more accessible for kids and smoking may impair driving or carry other risks, she said.

“But we’re already developing Oxycontin and Vicodin and teens are getting their hands on it,” she said.

If legalizing medical marijuana does help tackle the problem of painkiller deaths, that will be very significant, she said.

“Because opioid mortality is such a tremendously significant health crisis now, we have to do something and figure out what’s going on,” Hayes said.

The efforts states currently make to combat these deaths, like prescription monitoring programs, have been relatively ineffectual, she said.

“Everything we’re doing is having no effect, except for in the states that have implemented medical marijuana laws,” Hayes said.

People who overdose on opioids likely became addicted to it and are also battling other psychological problems, she said. Marijuana, which is not itself without risks, is arguably less addictive and almost impossible to overdose on compared to opioids, Hayes said.

Adults consuming marijuana don’t show up in the emergency room with an overdose, she said. “But,” she added, “we don’t put it in Rite Aid because we’re confused by it as a society.”

SOURCE: bit.ly/1pYZf8d JAMA Internal Medicine, August 25, 2014