Making medical marijuana legal does not prevent fatal opioid overdoses, study says

A new study shoots down the notion that medical marijuana laws can prevent opioid overdose deaths, challenging a favorite talking point of legal pot advocates.

Previous research linked medical marijuana laws to slower-than-expected increases in state prescription opioid death rates from 1999 to 2010. The scientists who published that work in the journal JAMA Internal Medicine in 2014 speculated that patients might be substituting marijuana for painkillers, though they warned against drawing conclusions.

Still, states ravaged by opioid overdose deaths began to rethink the role of marijuana, leading several to legalize pot for medical use.

So a team led by Chelsea Shover of Stanford University School of Medicine decided to update the analysis using data through 2017. When they did, they found the reverse: Death rates involving prescription opioids were 23% higher than expected in states that passed medical marijuana laws.

Legalizing medical marijuana “is not going to be a solution to the opioid overdose crisis,” said Shover, a postdoctoral scholar in psychiatry and behavioral sciences. “It would be wonderful if that were true, but the evidence doesn’t suggest that it is.”

Shover and her colleagues reported their findings Monday in the Proceedings of the National Academy of Sciences. They said it’s unlikely that medical marijuana laws caused first one big effect and then the opposite — any beneficial link was probably coincidental all along.

“We don’t think it’s reasonable to say it was saving lives before but it’s killing people now,” Stover said.

In the opioid crisis, dozens of forces are playing out across the nation in different ways. Among them: How widely available is the overdose antidote naloxone? Who has medical insurance, and does it cover addiction treatment?

What’s more, prescription painkillers once were involved in the largest share of overdose deaths, but that changed as heroin and then fentanyl surged. The studies on marijuana laws and opioid deaths don’t account for that.

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The new report undermines recent policy changes in some states. Last week, New Mexico joined New York, New Jersey and Pennsylvania in approving marijuana for patients with opioid addiction.

Experts agree evidence doesn’t support marijuana as a treatment for opioid addiction. Drugs like buprenorphine, morphine and naltrexone should be used instead, said Rosalie Liccardo Pacula, co-director of the Rand Drug Policy Research Center and co-author of a 2018 study on marijuana laws and overdose deaths.

The authors of the 2014 study welcomed the new analysis.

“We weren’t happy when a billboard went up saying marijuana laws reduce overdose deaths,” said Brendan Saloner of Johns Hopkins Bloomberg School of Public Health. “That was very hard for us to rein in.”

Marijuana has been shown to help ease chronic pain, and other studies have suggested medical marijuana laws may reduce opioid prescribing. So there’s still reason to believe that for some people, marijuana can substitute for opioids as a pain reliever.

As for addiction and the overdose crisis, “we should focus our research and policies on other questions that might make a difference,” Shover said.

Johnson is a writer for the Associated Press.