In a study of 777 people on methadone maintenance treatment, women who used cannabis were 82% more likely to also use illicit opioids, while no such association was found in men.
Read this if you or someone you know uses cannabis while on opioid treatment and wants to understand how it might affect recovery differently by sex.
Women using cannabis had 82% higher odds of illicit opioid use during methadone treatment
What the researchers found
Researchers studied 414 men and 363 women receiving methadone maintenance treatment for opioid use disorder across multiple clinics in Ontario, Canada. They found a striking sex difference in how cannabis use related to treatment outcomes.
Women who used cannabis during treatment were significantly more likely to also use illicit opioids compared to women who did not use cannabis. The association held after controlling for other variables, with cannabis-using women having 82% higher odds of illicit opioid use.
In men, no significant relationship between cannabis use and illicit opioid use was found. Notably, the heaviness of cannabis use (how much or how often) did not predict outcomes in either sex, suggesting it was any cannabis use, rather than the amount, that mattered for women.
Why it matters
Opioid use disorder treatment is a life-or-death matter, and identifying factors that predict relapse can help target interventions. The sex-specific nature of this finding suggests that treatment programs may need different approaches for men and women when it comes to addressing concurrent cannabis use. With cannabis legalization expanding, understanding these interactions becomes more urgent.
The numbers in context
777 participants total: 414 men and 363 women. Women using cannabis had 82% higher odds of illicit opioid use (OR = 1.82, 95% CI 1.18-2.82, p = 0.007). No significant association in men. Heaviness of cannabis use was not associated with outcomes in either sex.
How the study worked
This was a multicentre cross-sectional study recruiting participants from Canadian Addiction Treatment Centre sites in Ontario. Sex differences in the association between cannabis use and illicit opioid use were analyzed using multivariable logistic regression. A secondary analysis examined heaviness of cannabis use as a predictor.
What this study cannot tell us
The cross-sectional design cannot determine whether cannabis use causes opioid relapse or whether both behaviors reflect a common underlying factor. Self-reported cannabis and opioid use may be underreported. The study did not account for the reasons behind cannabis use (recreational versus self-medication). Results from Canadian clinics may not generalize to other settings.
How to read the evidence
This is a large cross-sectional study with appropriate statistical controls, but the observational design limits causal conclusions.
When this study was published
Published in 2017, before Canada's recreational cannabis legalization in 2018.
The bigger picture
This is one of the largest studies to examine sex differences in how cannabis use affects opioid treatment outcomes. It adds to a growing body of evidence that substance use patterns and treatment responses differ meaningfully between men and women, supporting the need for sex-specific treatment approaches in addiction medicine.
Questions still open
- What biological or social mechanisms explain why cannabis use is associated with opioid relapse in women but not men? Would addressing cannabis use in female methadone patients improve opioid treatment outcomes? Does the type of cannabis product or route of administration matter?
Common questions
Does this mean cannabis causes opioid relapse in women?
Why might sex matter for this relationship?
Read the original research
Association between cannabis use and methadone maintenance treatment outcomes: an investigation into sex differences.
Biology of sex differences, 8, 8
Citation
Zielinski, Laura; Bhatt, Meha; Sanger, Nitika; Plater, Carolyn; Worster, Andrew; Varenbut, Michael; Daiter, Jeff; Pare, Guillaume; Marsh, David C; Desai, Dipika; MacKillop, James; Steiner, Meir; McDermid Vaz, Stephanie; Thabane, Lehana; Samaan, Zainab. (2017). Association between cannabis use and methadone maintenance treatment outcomes: an investigation into sex differences.. Biology of sex differences, 8, 8. https://doi.org/10.1186/s13293-017-0130-1
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