By Pat Anson, PNN Editor

Illicit drug users who use cannabis for pain relief are less likely to experience an opioid overdose or use heroin, according to a Canadian study recently published in the online journal PLOS ONE.

Researchers at the University of British Columbia (UBC) the BC Centre on Substance Use (BCCSU) interviewed nearly 900 illicit drug users in Vancouver who reported using cannabis between 2016 and 2018. Participants were asked whether they used cannabis to relieve pain, improve sleep, address nausea or for recreation. Most said they used cannabis for a medically therapeutic reason.

"We're seeing more and more in our research that people are using cannabis for therapeutic reasons," says lead author Stephanie Lake, a doctoral candidate at UBC's School of Population and Public Health. "We're also seeing that, for some individuals in our study, this therapeutic use corresponds with either less use of illicit opioids or a reduced risk of overdose."

Participants who used cannabis for pain relief had lower odds of a non-fatal opioid overdose and for injecting heroin daily. Previous research from the BCCSU found that many people at risk of overdose, particularly those living with pain, may be using cannabis to reduce their reliance on illicit opioids.

Another key finding of the study was that therapeutic cannabis users relied on illicit sources for their cannabis supply – even though medical marijuana was fully legalized in Canada in 2013. About half of study participants said that illegal dispensaries were their most important source of cannabis.

"The mounting evidence related to the motivations behind people's cannabis use strongly suggests that improving access to cannabis for therapeutic purposes could help reduce overdose risk associated with illicit opioid use," says M.J. Milloy, PhD, a research scientist at BCCSU who was senior author of the study.

"Authorities should pause their efforts to close unregulated sources of cannabis and eliminate the illicit market until barriers to legal cannabis are addressed, especially during the overdose crisis."

Vancouver was the first major North American city to be hit by a wave of overdoses involving illicit fentanyl, heroin and other street drugs. A public health emergency was declared in British Columbia in 2016. Since then, Vancouver has become a laboratory of sorts for novel ways at addressing addiction, such as providing a “safe supply” of prescription opioids and prescription heroin to illicit drug users.

“Our community and many others across Canada and the United States are experiencing an opioid overdose crisis rooted, in part, in inadequately or inappropriately-managed chronic pain and sparked by widespread exposure to an unregulated illicit opioid supply contaminated with potent opioid analogues,” researchers concluded. “Our finding may also reflect an opioid-sparing effect of cannabis, whereby opioids are not replaced, but the dosage or frequency of opioid required for analgesia is reduced with the use of cannabis.”

Other studies have debunked the idea that medical cannabis reduces opioid use. Two large studies published last year found no evidence that legalizing cannabis reduces prescription opioid use, overdose or mortality.

“We tested this relationship and found no evidence that the passage of medical marijuana laws — even in states with dispensaries — was associated with a decrease in individual opioid use of prescription opioids for nonmedical purposes," researchers found.

A 2018 study suggested that cannabis legalization could actually make the opioid crisis worse, concluding that “cannabis use appears to increase rather than decrease the risk of developing nonmedical prescription opioid use and opioid use disorder.”