The effectiveness of cannabis as a tool to combat the opioid epidemic has been called into question by a new study.
In 2014, a study was published that showed states which had moved to legalize medical marijuana had seen a nearly 25 percent reduction in opioid-related deaths. The findings led researchers to cautiously speculate that liberalized cannabis laws may be associated with the decreased death rates noted in these states. However, they noted their research did not prove a causal relationship.
Still, the study galvanized a movement that began to see safe access to medical marijuana as key to fighting the country's opioid epidemic.
But, when a recent study out of Stanford University tried to recreate and expand on the 2014 research, they found the number of opioid-related deaths eventually swung back up.
"A lot of people treated it as evidence that medical cannabis could reverse the opioid crisis," Chelsea Shover—the new study's lead author—said of the 2014 study. "But does that really hold up over time? In short, what we found was no."
The original study looked at data collected between 1999 and 2010. During that time, only 13 states had legalized medical marijuana. The new study extended the time span up to 2017 - when 47 states had legalized some form of medical marijuana. And while the new research also found that in the 1999–2010 period opioid related deaths certainly did drop by over 20 percent, from 2010–2017 they began to rise again.
"What we found was that association between enacting a medical cannabis law and the rate of deaths from opioid overdose actually reversed over time," Shover said. "When we did the study in 2017, the association was that states that enacted a medical cannabis law actually had higher opioid overdose deaths after the laws took effect."
Shover suggests that these contradictory findings mean that cannabis regulations likely have little to no impact on the opioid crisis.
"We don’t think cannabis was saving lives at the population level 10 years ago, and we don’t think it’s killing people now," Shover said. "We think these two factors are separate issues."
Instead, Shover suggests that it was other characteristics of the early medical marijuana states that accounted for the reduction in opioid deaths. Most of these were "western, politically liberal states" and the opioid epidemic was disproportionately growing in other regions.
"I think that shared characteristics between those 13 states—things like less incarceration of people using drugs, more availability of treatment for opioid use disorder, and more availability of the overdose reversal drug naloxone—explain the association they found," Shover added.
However, Brendan Saloner - one of the authors of the 2014 study - has also suggested that the changing nature of the ongoing opioid epidemic may have reduced the effectiveness of cannabis as a potential treatment of opioid use disorder.
"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," Saloner said.
"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."
Saloner's co-author Chinazo Cunningham spoke up to defend their original findings as well. While she admitted that "certainly cannabis is not a silver bullet," she also noted that there are other studies which have made similar findings to theirs.
It's also worth noting that the study's sample size could be undermining its conclusions. While 47 states have legalized some form of medical cannabis, access varies widely between those jurisdictions. In fact, 14 of those states only allow CBD oil to be used, so patients can't get dried flower, edibles, topicals or other cannabis products - especially ones containing THC, which has been shown to have medicinal value. On top of that, states like Texas, Virginia and several others only allow CBD oil to be used for intractable epilepsy. So it's not surprising that medical marijuana has failed to combat the opioid epidemic in states where it is available in a limited form for a single condition.
Ultimately, what all of these researchers agree on is that the conflicting data just proves more research needs to be done. And until the federal government stops hampering efforts to study the benefits of cannabis, we won't get a chance to thoroughly examine the role that medical marijuana could play in combating the opioid epidemic.