“Ecological research suggests that increased access to cannabis may facilitate reductions in opioid use and harms, and medical cannabis patients describe the substitution of opioids with cannabis for pain management.

We aimed to investigate the longitudinal association between frequency of cannabis use and illicit opioid use among people who use drugs (PWUD) experiencing chronic pain.

The most commonly reported therapeutic reasons for cannabis use were pain (36%), sleep (35%), stress (31%), and nausea (30%). After adjusting for demographic characteristics, substance use, and health-related factors, daily cannabis use was associated with significantly lower odds of daily illicit opioid use (adjusted odds ratio 0.50, 95% CI 0.34-0.74, p < 0.001).

We observed an independent negative association between frequent cannabis use and frequent illicit opioid use among PWUD with chronic pain. These findings provide longitudinal observational evidence that cannabis may serve as an adjunct to or substitute for illicit opioid use among PWUD with chronic pain.”

https://www.ncbi.nlm.nih.gov/pubmed/31743343

“In conclusion, we found evidence to suggest that frequent use of cannabis may serve as an adjunct to or substitute for illicit opioid use among PWUD with chronic pain in Vancouver. The findings of this study have implications for healthcare and harm reduction service providers. In chronic pain patients with complex socio-structural and substance use backgrounds, cannabis may be used as a means of treating health problems or reducing substance-related harm. In the context of the current opioid crisis and the recent rollout of a national regulatory framework for cannabis use in Canada, frequent use of cannabis among PWUD with pain may play an important role in preventing or substituting frequent illicit opioid use.”

https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1002967