Cannabis Use Doubled the Risk of Starting Heavy Drinking Among People Who Use Heroin
In a Vancouver cohort of 357 heroin users, cannabis use was the strongest independent predictor of initiating heavy drinking, doubling the risk, while methadone treatment did not increase heavy drinking.
Quick Facts
What This Study Found
There has been concern that people entering methadone maintenance therapy (MMT) for heroin addiction might substitute alcohol for heroin. This study followed 357 heroin users in Vancouver for up to 9 years to test this hypothesis.
Methadone treatment did not predict heavy drinking initiation. In fact, those enrolled in MMT at some point had lower heavy drinking rates than those who never enrolled (4.6 vs. 16.2 per 100 person-years).
The surprise finding was about cannabis. Cannabis use was independently associated with a 2.06-fold increased risk of initiating heavy drinking, making it the strongest substance-use predictor in the model. Younger age was the only other significant predictor.
Key Numbers
357 heroin users followed. 208 (58%) enrolled in MMT during follow-up. 115 (32%) initiated heavy drinking. Incidence: 7.8 per 100 person-years overall. MMT enrolled: 4.6 vs. not enrolled: 16.2 per 100 person-years. Cannabis use: adjusted HR = 2.06 (95% CI 1.32-3.19). Younger age: adjusted HR = 0.74 per 10 years.
How They Did This
Prospective community-based cohort study of people who inject drugs in Vancouver, Canada, from December 2005 to May 2014. Extended Cox regression analysis examined the effect of methadone enrollment on heavy drinking onset, controlling for demographic and substance-use characteristics.
Why This Research Matters
This study provides two important findings: methadone treatment does not drive heroin users toward heavy drinking (a concern that could discourage treatment), and cannabis use is a surprisingly strong predictor of heavy drinking in this population. The cannabis finding suggests potential cross-substance vulnerability.
The Bigger Picture
The finding that cannabis use predicts heavy drinking initiation among heroin users adds to growing evidence of polysubstance vulnerability. It suggests that clinicians treating opioid use disorder should also monitor cannabis and alcohol use patterns.
What This Study Doesn't Tell Us
Observational study cannot establish causation. Cannabis use might be a marker for broader substance use vulnerability rather than a direct cause of heavy drinking. Self-reported substance use data. Vancouver's unique drug policy context may limit generalizability.
Questions This Raises
- ?Why does cannabis use predict heavy drinking in heroin users?
- ?Is cannabis use a general marker of polysubstance vulnerability, or does it specifically increase alcohol risk?
- ?Should opioid treatment programs screen for and address cannabis use?
Trust & Context
- Key Stat:
- Cannabis use doubled the risk of heavy drinking initiation (HR = 2.06)
- Evidence Grade:
- Prospective cohort design with extended Cox regression and multiple confounders controlled. Good methodology but observational limitations.
- Study Age:
- Published in 2016 using data from 2005-2014. The opioid crisis and treatment landscape have evolved significantly.
- Original Title:
- The Impact of Enrolment in Methadone Maintenance Therapy on Initiation of Heavy Drinking among People Who Use Heroin.
- Published In:
- European addiction research, 22(4), 210-4 (2016)
- Authors:
- Klimas, Jan(2), Wood, Evan(8), Nguyen, Paul, Dong, Huiru, Milloy, Michael John, Kerr, Thomas, Hayashi, Kanna
- Database ID:
- RTHC-01196
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
Does methadone treatment lead to heavy drinking?
No. This study found no evidence that entering methadone treatment increased heavy drinking risk among heroin users. Rates were actually lower among those in treatment.
Why is cannabis use linked to heavy drinking in heroin users?
Cannabis use doubled the risk of initiating heavy drinking in this population, though whether this reflects a causal relationship or shared vulnerability to substance use is unknown.
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Cite This Study
https://rethinkthc.com/research/RTHC-01196APA
Klimas, Jan; Wood, Evan; Nguyen, Paul; Dong, Huiru; Milloy, Michael John; Kerr, Thomas; Hayashi, Kanna. (2016). The Impact of Enrolment in Methadone Maintenance Therapy on Initiation of Heavy Drinking among People Who Use Heroin.. European addiction research, 22(4), 210-4. https://doi.org/10.1159/000444513
MLA
Klimas, Jan, et al. "The Impact of Enrolment in Methadone Maintenance Therapy on Initiation of Heavy Drinking among People Who Use Heroin.." European addiction research, 2016. https://doi.org/10.1159/000444513
RethinkTHC
RethinkTHC Research Database. "The Impact of Enrolment in Methadone Maintenance Therapy on ..." RTHC-01196. Retrieved from https://rethinkthc.com/research/klimas-2016-the-impact-of-enrolment
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.