“We saw a 9% or 10% reduction (in opioid prescriptions) in Colorado and Oregon,” Wen said. “And in Alaska and Washington, the magnitude was a little bit smaller but still significant.”
The first state in the United States to legalize marijuana for medicinal use was California, in 1996. Since then, 29 states and the District of Columbia have approved some form of legalized cannabis. All of these states include chronic pain — either directly or indirectly — in the list of approved medical conditions for marijuana use, according to Bradford.
The details of the medical cannabis laws were found to have a significant impact on opioid prescription patterns, the researchers found. States that permitted recreational use, for example, saw an additional 6.38% reduction in opioid prescriptions under Medicaid compared with those states that permitted marijuana only for medical use, according to Wen.
The method of procurement also had a significant impact on opioid prescription patterns. States that permitted medical dispensaries — regulated shops that people can visit to purchase cannabis products — had 3.742 million fewer opioid prescriptions filled per year under Medicare Part D, while those that allowed only home cultivation had 1.792 million fewer opioid prescriptions per year.
“We found that there was about a 14.5% reduction in any opiate use when dispensaries were turned on — and that was statistically significant — and about a 7% reduction in any opiate use when home cultivation only was turned on,” Bradford said. “So dispensaries are much more powerful in terms of shifting people away from the use of opiates.”
The impact of these laws also differed based on the class of opioid prescribed. Specifically, states with medical cannabis laws saw 20.7% fewer morphine prescriptions and 17.4% fewer hydrocodone prescriptions compared with states that did not have these laws, according to Bradford.
Fentanyl prescriptions under Medicare Part D also dropped by 8.5% in states that had enacted medical cannabis laws, though the difference was not statistically significant, Bradford said. Fentanyl is a synthetic opioid, like heroin, that can be prescribed legally by physicians. It is 50 to 100 times more potent than morphine, and even a small amount can be fatal, according to the National Institute on Drug Abuse
“I know that many people, including the attorney general, Jeff Sessions, are skeptical of cannabis,” Bradford said. “But, you know, the attorney general needs to be terrified of fentanyl.”
‘A call to action’
This is not the first time researchers have found a link between marijuana legalization and decreased opioid use. A 2014 study
showed that states with medical cannabis laws had 24.8% fewer opioid overdose deaths between 1999 and 2010. A study in 2017
also found that the legalization of recreational marijuana in Colorado in 2012 reversed the state’s upward trend in opioid-related deaths.
“There is a growing body of scientific literature suggesting that legal access to marijuana can reduce the use of opioids as well as opioid-related overdose deaths,” said Melissa Moore
, New York deputy state director for the Drug Policy Alliance. “In states with medical marijuana laws, we have already seen decreased admissions for opioid-related treatment and dramatically reduced rates of opioid overdoses.”
Some skeptics, though, argue that marijuana legalization could actually worsen the opioid epidemic. Another 2017 study
, for example, showed a positive association between illicit cannabis use and opioid use disorders in the United States. But there may be an important difference between illicit cannabis use and legalized cannabis use, according to Hill.
“As we have all of these states implementing these policies, it’s imperative that we do more research,” Hill said. “We need to study the effects of these policies, and we really haven’t done it to the degree that we should.”
The two recent studies looked only at patients enrolled in Medicaid and Medicare Part D, meaning the results may not be generalizable to the entire US population.
But both Hill and Moore agree that as more states debate the merits of legalizing marijuana in the coming months and years, more research will be needed to create consistency between cannabis science and cannabis policy.
“There is a great deal of movement in the Northeast, with New Hampshire and New Jersey being well-positioned to legalize adult use,” Moore said. “I believe there are also ballot measures to legalize marijuana in Arizona, Florida, Missouri, Nebraska and South Dakota as well that voters will decide on in Fall 2018.”
Hill called the new research “a call to action” and added, “we should be studying these policies. But unfortunately, the policies have far outpaced the science at this point.”