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PLoS Med. 2019 Nov 19;16(11):e1002967. doi: 10.1371/journal.pmed.1002967. eCollection 2019 Nov.

Frequency of cannabis and illicit opioid use among people who use drugs and report chronic pain: A longitudinal analysis.

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British Columbia Centre on Substance Use, Vancouver, British Columbia, Canada.
School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Psychology, University of British Columbia, Kelowna, British Columbia, Canada.
Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, California, United States of America.
British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
Department of Family Medicine, McGill University, Montreal, Québec, Canada.
Department of Anesthesia, McGill University, Montreal, Québec, Canada.



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. However, there is a lack of research using individual-level data to explore this question. 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.


This study included data from people in 2 prospective cohorts of PWUD in Vancouver, Canada, who reported major or persistent pain from June 1, 2014, to December 1, 2017 (n = 1,152). We used descriptive statistics to examine reasons for cannabis use and a multivariable generalized linear mixed-effects model to estimate the relationship between daily (once or more per day) cannabis use and daily illicit opioid use. There were 424 (36.8%) women in the study, and the median age at baseline was 49.3 years (IQR 42.3-54.9). In total, 455 (40%) reported daily illicit opioid use, and 410 (36%) reported daily cannabis use during at least one 6-month follow-up period. 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). Limitations of the study included self-reported measures of substance use and chronic pain, and a lack of data for cannabis preparations, dosages, and modes of administration.


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.

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Conflict of interest statement

I have read the journal's policy and the authors of this manuscript have the following competing interests: M-JM is the Canopy Growth professor of cannabis science at UBC, a position created using unstructured arms’ length gifts to the university from Canopy Growth Corporation and the Government of British Columbia’s Ministry of Mental Health and Addictions. The University of British Columbia has received unstructured funding from NG Biomed, Ltd., an applicant to the Canadian federal government for a license to produce cannabis, to support M-JM. ZW is Coordinating Principal Investigator on a clinical trial sponsored by Tilray, a licensed producer of medical cannabis. ZDC has received research funds and partial salary support from Insys Therapeutics. She has served as a consultant to GB Sciences and Beckley Canopy Therapeutics and is a scientific advisor to FSD Pharma. MAW has consulted for CHI, CannaRoyalty and Zynerba and has received a grant to his institution for clinical research from CanniMed. He was appointed to Chief Medical Officer at Canopy Growth Corp in July 2018 (after the study period ended). He supported the first author in conceptualization of the research, but did not contribute to the study’s methodological design or data analysis. All other authors report no competing interests in relation to the work described.

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