Can medical marijuana reduce fatal opioid overdoses? Maybe not.

A study published Monday in the Proceedings of the National Academy of Sciences casts doubt on claims that medical marijuana legalization could reduce opioid-related overdose deaths.

New resource guide: Medical marijuana in the health system

Background

Amid the United States' opioid epidemic, public health officials and policymakers have been searching for non-opioid alternatives for treating chronic pain. Previous studies have suggested medical marijuana could be an effective option and found a link between medical marijuana legalization and a decrease in opioid-related overdose deaths, according to the Washington Post's "PowerPost."

For example, Vox reports a "widely cited" 2014 study conducted by researchers at the Johns Hopkins Bloomberg School of Public Health found states that had legalized medical marijuana reported a nearly 25% lower mean annual opioid overdose mortality rate from 1999 to 2010, when compared with states that had not legalized medical marijuana. The researchers arrived at those findings by comparing death certificates with opioid overdose death rates in states with and without laws legalizing medical marijuana.

New research finds conflicting results

But in a follow up study, Stanford University researchers discovered that trend began to reverse after 2010. The researchers used the same methods and dataset as the Johns Hopkins researchers, only they had more data at their disposal, extending through 2017 and including states that had newly legalized medical marijuana.

The Stanford researchers similarly found a 21% decrease in opioid-related overdose deaths for every 100,000 people in the population when states legalized medical marijuana between 1999 and 2010. However, when they examined data from 1999 to 2017, they found a 23% increase in opioid overdose deaths in states that had legalized medical marijuana.

Chelsea Shover of the Stanford University School of Medicine in California, who was the study's lead author, said, "With the benefit of a longer time span ... we conclude that medical cannabis laws do not seem to have reduced opioid overdose mortality at the population level."

However, Shover added, the researchers also do not believe legalizing medical marijuana fueled the opioid epidemic. Shover and her team now believe it is unlikely legalizing medical marijuana had any significant causal effect on opioid overdose death rates, and any previous link might have been coincidental.

Instead, the researchers said other factors could explain the shift in the correlation between opioid overdose deaths and medical marijuana legalization. Shover explained that, at the time of the first study, only 13 states had medical marijuana laws, and most of them were in the west. Those states "shared characteristics … like less incarceration of people using drugs, more availability of treatment for opioid use disorder, and more availability of the overdose reversal drug naloxone," according to Shover.

When it comes to addressing the opioid epidemic, Shover said marijuana reforms "should still absolutely be considered" but, more broadly, "[w]e should focus our research and policies on other questions that might make a difference."

'Surprising' results

Brendan Saloner, a co-author of the 2014 study and a researcher at Johns Hopkins' Bloomberg School of Public Health, said the results of the new study were surprising. "I was not expecting this finding, but I think that it could plausibly be explained by the changing nature of the opioid crisis," Saloner said.

She continued, "Specifically, heroin and fentanyl have been involved in a lot more overdose deaths—including deaths that also involve prescription opioids—and that could reduce the protective effect of medical cannabis. Second, the states implementing medical cannabis laws, and the way these laws have been implemented, has been changing over time, and it may be that they are getting less effective at reducing harmful opioid use" (Winfield Cunningham, "PowerPost," Washington Post, 6/11; Lopez, Vox, 6/11; Rapaport, Reuters, 6/10; Johnson, AP/Los Angeles Times, 6/10).

Resource guide: Medical marijuana in the health system

Despite the legal and clinical ambiguity surrounding marijuana policy and use, health systems should devise a strategy for managing marijuana in their facilities. Use these resources to inform and develop your system's strategy.

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