Since the 2014 release of a study that suggested that states with medical marijuana programs had fewer opioid overdose deaths, proponents of legalized cannabis have argued that it can help save lives amid the opioid crisis. 

A new, broader study released this week, however, has found that states with medical cannabis programs actually have 23% more opioid overdose deaths than states without medical cannabis. The new results called into concern efforts to paint marijuana legalization as a solution to opioid abuse. 

“It’s become such a pervasive idea. It would be amazing if it was this simple, but the evidence is telling us now that it’s not,” lead author Chelsea Shover told STAT News

The original study looked at the years 1999 through 2010. During that time, 13 states had medical marijuana programs, and the study found that those states had opioid overdose rates that were 25% lower than states without medical cannabis. 

When Shover’s team replicated that study, they found the same results in that time period. However, they then expanded the study, looking at years through 2017. During that time, many more states implemented medical cannabis programs, and a handful introduced legalized recreational cannabis.

During that time period, the researchers found that states with legal medical cannabis actually had higher overdose rates. 

“Not only did findings from the original analysis not hold over the longer period, but the association between state medical cannabis laws and opioid overdose mortality reversed direction from−21% to +23% and remained positive after accounting for recreational cannabis laws,” study authors wrote

The authors of the new study concluded that the apparent connection between legalized cannabis and opioid overdose deaths was “spurious,” or false.  

“We find it unlikely that medical cannabis—used by about 2.5% of the U.S. population—has exerted large conflicting effects on opioid overdose mortality,” study authors wrote. 

Shover emphasized this point. “This isn’t to say that cannabis was saving lives 10 years ago and it’s killing people today,” she said. “We’re saying these two things are probably not causally related.”

Because opioids and medical marijuana are both commonly used to treat pain, the theory went that people with access to cannabis for pain relief were less likely to get hooked on addictive opioids. Today, states including Illinois allow people to substitute medical marijuana for conditions that they otherwise would be given opioids for. This is based on the assumption that cannabis is safer—and less addictive—than opioids. 

Neuroscientist Yasmin Hurd, who directs the Addiction Institute at Mount Sinai in New York, said that further large-scale research is needed to examine the link—if any—between access to cannabis and opioid overdoses. 

“In a time of an epidemic, we have to think differently,” she said. “We have to be more bold in pushing forward clinical trials on a much faster timeline than we have in the past.”

Although she agreed that cannabis is less dangerous than opioids, she said that marijuana policy should not be pushed forward as a harm reduction strategy for opioids. 

She said, “Is cannabis less of a mortality risk than opioids? Absolutely. Hands down. But there’s really no research that says cannabis use per se decreases opioid overdose. You can’t make your medical cannabis laws based on that [hypothesis].”

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