When a 2014 study in JAMA Internal Medicine found that states with medical cannabis laws had lower opioid overdose death rates than states without such laws, some policymakers and advocates of medical cannabis interpreted the findings to mean that medical cannabis could help address the opioid crisis. Several states went so far as to approve medical cannabis as a treatment for opioid use disorder (OUD). Now a study in Proceedings of the National Academy of Sciences (PNAS) suggests that legalizing medical cannabis has not lowered opioid-related death rates after all.

The earlier study, which included data from 1999 through 2010, found that states experienced a 24.8% reduction in opioid overdose deaths after introducing medical cannabis laws. When the researchers in the PNAS study, who used the same methods, included data collected through 2017, they found that states with medical cannabis laws experienced a 22.7% increase in opioid overdose deaths between 1999 and 2017.

The downstream effect of using cannabis to treat opioid use disorder is that patients who could benefit from evidence-based treatment do not receive it. —Smita Das, M.D.

Yet that doesn’t mean that the laws increased opioid deaths, said Chelsea L. Shover, Ph.D., a postdoctoral research fellow in psychiatry at Stanford University and lead author of the PNAS study.

“To have that dramatic a swing over a seven- or eight-year period says these two things [opioid overdose deaths and medical cannabis laws] aren’t really related. There are other variables and factors related to opioid overdose, like socioeconomic status, regional differences, or incarceration. I don’t think our paper would or should make any difference in how states regulate cannabis,” Shover said.

Shover expressed apprehension that some legislators, cannabis proponents, and patients will continue to see medical cannabis as a way of treating OUD, particularly because it is virtually impossible for a cannabis overdose to be fatal.

The dramatic swing in opioid mortality implies that opioid-related death rates are unrelated to medical cannabis laws, says Chelsea L. Shover, Ph.D. Frerk Hopf

“But that doesn’t mean it’s a substitute for the treatments we do have, like buprenorphine and methadone, and seeing medical cannabis used that way is concerning,” Shover said.

Smita Das, M.D., M.P.H., a member of APA’s Council on Addiction Psychiatry, noted the potential risks of substituting medical cannabis for treatments approved by the Food and Drug Administration. “The downstream effect is that people who would benefit from evidence-based treatment may resort to non–evidence-based approaches such as cannabis, which means we’re undertreating people who could benefit from methadone and buprenorphine,” said Das, who was not involved in the research.

“Anywhere from 10% to 30% of people who use cannabis end up developing cannabis use disorder. I am concerned with using a substance that can cause addiction to treat another addiction, especially when we have very good evidence-based methods of treating OUD,” Das added.

Last fall, APA published a resource document prepared by the Council on Addiction Psychiatry in opposition to the use of cannabis as medicine. It is posted here.

Shover called for additional research before considering medical cannabis as a potential treatment for OUD. “This is a good reminder to look at what there is evidence for and what there is no evidence for. We need prospective data collected on an individual level where some people on opioids use cannabis to try to get off of opioids and some don’t, and you see who has better outcomes,” Shover said.

However, such a trial would be a challenge, Shover added. “It’s tough to do cannabis studies that produce high-quality evidence. The Drug Enforcement Administration has loosened up a little in recent years [concerning cannabis study requirements], but there are still very few people who are able to do the research,” Shover said.

In the meantime, Das encourages psychiatrists to foster open communication with patients about what substances they are using. “Regardless of whether it’s illicit or not, how we ask questions about substance use is what helps patients be comfortable. Rather than ask, ‘Do you use cannabis?’ I ask, ‘When was the last time you used cannabis?’” Das said. “Rather than push the patient one way or the other, understand where they’re coming from and what they’re dealing with,” Das added. “There may be a problem associated with cannabis, and when the patient is ready to talk about it and consider cutting down, we talk about choices. My job is to provide the information and make sure the patient knows the data.”

This study was supported by the National Institute on Drug Abuse, the Wu Tsai Neurosciences Institute, the Veterans Health Administration, and Stanford University. ■