Marijuana legalization advocates say cannabis can play a role in battling opioid dependency, but the science behind the claim appears to have become outdated.

The theory makes sense, though. Cannabis has been shown to help relieve chronic, non-debilitating pain, and prescription opioid abuse often begins unintentionally following chronic pain treatment. Marijuana also provides euphoria and a high that one would expect could be utilized as substitutes for the opioid analog.

A 2010-13 study conducted by the University of Georgia found that doctors in states with medical cannabis programs prescribed a significantly lower number of painkillers than those in other states. The study reviewed prescriptions filled through Medicare Part D and found that the average doctor in these states prescribed 1,826 fewer daily doses of painkillers per year on average than doctors in states with no medical cannabis program.

But the real buzz around the idea came in 2014, when a JAMA study conducted by researchers at the University of Pennsylvania found that opioid-related deaths declined in states that had medical cannabis programs of some sort. The study struck a chord in the mainstream, and advocates began to pull it out during every conversation.

Problems With the Theory

But something happened when a 2019 study published in Proceedings of the National Academy of Sciences of the United States of America tried to replicate the 2014 study. It surprisingly produced results that showed the opposite of the original. The authors were able to replicate the original results when they used the first study’s timeline: 1999 to 2010. But the results changed when they added data through 2017. With the expanded data, they found that opioid deaths actually increased by 23 percent in states that had medical cannabis laws.

Just think of our own state. Despite having over 100,000 cannabis patients registered with the New Mexico Medical Cannabis Program, one of the oldest in the U.S., we have one of the worst opioid dependency problems in the nation. In 2018 63 percent of drug overdoses in New Mexico were attributed to opioids—a total of 338 deaths—a rate of 16.7 per 100,000 people, compared to the national rate of 14.6 at that time. The number of opioid prescriptions trailed behind the national average but still came in at an incredible rate of 49.4 prescriptions per 100 people—nearly half the population was prescribed these highly addictive substances that year. Street opioids like heroin made up the difference by killing 130 people in New Mexico at a rate of 6.6 per 100,000, compared to the national rate of 4.7. This was five years after the Medical Cannabis Program was initiated.

According to the state attorney general’s website, New Mexico had the third highest drug overdose death rate in the nation in 2013, the second highest in 2014 and remained in the highest age-adjusted rate category in the nation in 2015.

Lead author of the PNAS paper Chelsea Shover, a postdoctoral research fellow in psychiatry at Stanford, told reporters, “This isn’t to say that cannabis was saving lives 10 years ago and it’s killing people today,” said Shover. “We’re saying these two things are probably not causally related.”

In a 2019 study published in the journal CMAJ Open, researchers analyzed data from 23 studies that looked at the use of cannabis in conjunction with methodone therapy to treat opioid dependency. The authors found “no consensus among studies that cannabis use is associated with reduced opioid use or longer treatment retention when used during methadone maintenance therapy.” The paper criticized the studies for being low in scientific value as well. “The overall quality of evidence was very low, with a high risk of bias, owing to the nature of observational studies,” the authors wrote.

In fact, other studies have even found that medical cannabis patients are supposedly more likely to use opioids—prescription and illicit. A 2018 study from the Journal of Addiction Medicine found that patients enrolled in medical cannabis programs were more likely to report using prescription drugs than others, and a paper published in 2015 in Drug and Alcohol Dependence found that cannabis patients might require more pain medications than nonusers as the drugs seem to have less affect on marijuana users. A 2017 study from the American Journal of Psychiatry even discovered that using marijuana statistically correlates with an increased chance of developing an opioid use disorder.

The results from all of these studies appear to contradict each other in every way. So it seems that we might be dealing with the common mistake of implying causation from correlation. As the famous raven paradox highlights: Some birds are black, but not all birds are blackbirds.

Cannabis As Pain Management Alternative

This means that on the macro level of society at large, cannabis legalization might not be the easy answer to the opioid epidemic that we were hoping for. On the micro level, though—at the personal level of the individual—there is still a good chance that marijuana’s efficacy as an analgesic could help victims of chronic pain avoid addiction by using cannabis instead of turning to opioids in the first place.