People Who Inject Opioids Are Less Likely to Overdose If Also Using Cannabis for Pain, Study Finds

People who inject drugs such as heroin have a lower chance of accidentally overdosing if they’re also using cannabis to manage their pain, according to a new study.

As most of the study’s participants used cannabis for pain relief, many also reduced their reliance on heroin and illicit opioids, which reduced their risk of an overdose.

The findings add further weight to the case for using medical cannabis as a substitute for illicit opioids.

Cannabis in Vancouver

Published in PLOS One, the study gleaned its results from two ongoing research groups living in Vancouver's Downtown Eastside.

One group consisted of HIV-negative people who inject drugs, while the other was made up of those living with HIV. Both cohorts have been monitored by researchers since 1996.

After conducting 2,500 interviews, the researchers from the University of British Columbia classed over two thirds (68.4 percent) of the 897 participants as therapeutic cannabis consumers.

Members of this therapeutic group tended to exhibit poorer indicators of health than those classed as recreational users. But this negative association, the researchers say, is likely indicative of cannabis being used to address poor health rather than poor health resulting from frequent cannabis use.

The participants who used cannabis to relieve pain also had lower odds of reporting a recent non-fatal overdose and daily heroin injection relative to the other classes. The opioids weren’t fully replaced by cannabis in most cases. Instead, participants used the opioids less frequently if also treating themselves with cannabis.

The results add to the growing body of evidence for marijuana’s suitability as an opioid substitute.

“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,” Dr M-J Milloy, a substance use researcher at the University of British Columbia and senior author of the study, said in a statement.

“Unfortunately, our results also tell us that medical cannabis users from the Downtown Eastside do not have equitable access to legal sources of cannabis, either through the medical cannabis system or the new recreational market.”

Indeed, even though Vancouver residents have had legal medical cannabis access since 2001 and legal recreational access since 2018, Milloy and his colleagues found few instances where participants had sourced their cannabis legally. This strong reliance on the illicit market highlights how Canada’s legal cannabis framework still has many access barriers for “marginalized people.”

“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,” Milloy added.