Recent studies on the relationship between marijuana laws and opioid use have generally reached a consistent conclusion: when people have legal access to medical cannabis, they use opioids less often.
But a new meta-analysis of 25 separate ecological and epidemiological studies on the subject also reveals a need to conduct rigorous clinical trials on humans to verify and further understand this effect.
The purpose of the review was to “assess how convincing” the evidence reported in previous studies—that legal cannabis laws are associated with lower rates of opioid use and overdose—really is. The researchers behind the new paper, published this month in the International Journal of Psychiatry, focused exclusively on ecological and epidemiological studies and excluded many others from their analysis due to various limitations such as concurrent cannabinoid and opioid administration.
Both kinds of research turned up “mixed support for pre-clinical evidence that the use of cannabis for medical purposes may reduce opioid use.” Ecological studies in particular have shown that people die from opioid overdoses at a slower rate in legalized states.
“In ecological studies, states that allow medical cannabis laws have reported a slower rate of increase in opioid overdose deaths compared with states without such laws,” the review found. “These differences have increased over time and persisted after controlling for state sociodemographic characteristics and use of prescription monitoring programmes.”
The researchers made a series of recommendations for future studies to bolster evidence derived from pre-clinical studies. Studies should look at chronic pain patients who use opioids to explore whether access to cannabis leads them to reduce their dose of painkillers or other substances. Similar data should be collected on people who misuse opioids. Also, researchers should broadly study chronic pain patients who use medical cannabis for pain management.
“If cannabis use reduced overdose deaths in pain patients or people who use opioids non-medically, this would represent a public health gain, albeit by different mechanisms with very different policy implications,” the study authors wrote.
“In conclusion, both ecological and epidemiological evidence suggest that the availability and use of cannabis for medical purposes may be associated with reduced opioid use and related harms. At this point the findings are not conclusive, and clear evidence of causality is lacking… Well-conducted clinical studies are needed to measure any opioid-sparing effects of cannabis, and to assess the prevalence of any adverse or unintended effects of using cannabinoids.”
While a relatively small number of studies ultimately fell within the parameters of this analysis, research on cannabis and opioids has rapidly expanded in recent years—due in no small part to the explosion of the opioid crisis—and the evidence has widely supported the idea that cannabis can reduce the harms of the drug problem.
Photo courtesy of M a n u e l.