Summary: A McMaster University review found no evidence that cannabis helps people with opioid use disorder stop using opioids while receiving methadone maintenance treatment.
Source: McMaster University
Key finding: Interest has grown in whether cannabis could serve as a substitute or “exit drug” for people with opioid use disorder, but a systematic review and meta-analysis from McMaster University shows no reliable evidence that cannabis use reduces illicit opioid use or improves retention in methadone maintenance therapy.
The research team conducted a comprehensive review of published studies that examined how cannabis use relates to illicit opioid use among patients undergoing methadone maintenance therapy, a common medication-assisted treatment for opioid dependence. In total, the authors included 23 studies in their systematic review and carried out a meta-analysis on six of those studies that together involved 3,676 participants.
Meta-analysis results indicated that cannabis use during methadone treatment was not associated with a reduction in illicit opioid use, nor did it improve treatment retention. The studies showed substantial variability in methods and outcomes, and the authors judged the overall quality of the evidence to be very low due to the observational nature of the included studies and high risk of bias.
“There is limited evidence that cannabis use may reduce opioid use in pain management, and some high-profile organizations have suggested cannabis is an ‘exit drug’ for illicit opioid use, but we found no evidence to suggest cannabis helps patients with opioid use disorder stop using opioids,” said senior author Dr. Zainab Samaan, associate professor of psychiatry and behavioural neurosciences at McMaster and a Hamilton staff psychiatrist.
The study’s methods followed standard systematic review practice. The investigators searched multiple databases up to July 12, 2018, including MEDLINE/PubMed, Embase, PsycINFO, CINAHL and ProQuest Dissertations and Theses Global. They summarized how cannabis use affected illicit opioid consumption and whether cannabis was associated with longer retention in methadone maintenance programs. For pooled analyses they used a random effects meta-analysis model but reported that high heterogeneity across studies limited the strength of pooled estimates; forest plots were provided by the authors as supplemental material.
Results from the six studies included in the quantitative synthesis did not demonstrate a clear benefit of cannabis use for reducing opioid use during methadone maintenance therapy. Because the studies varied in design, population and measurement of cannabis and opioid use, the authors emphasize caution in interpreting findings and note the overall low certainty of evidence. Observational designs and potential confounding factors contributed to the high risk of bias assessment.
Funding: The research was supported by the Canadian Institutes of Health Research.
Source:
McMaster University
Media Contacts:
Veronica McGuire – McMaster University
Image Source:
The image is in the public domain.
Original Research: Closed access
“Cannabis use during methadone maintenance treatment for opioid use disorder: a systematic review and meta-analysis.” Zainab Samaan et al., Canadian Medical Association Journal. DOI: 10.9778/cmajo.201900266.
Abstract summary: The review assessed whether cannabis use is associated with reduced opioid use or greater retention in methadone maintenance programs. Twenty-three studies were included in the review and six were suitable for meta-analysis (total n = 3,676). High heterogeneity and methodological limitations produced very low-quality evidence. The authors conclude there is no consistent support for cannabis as an effective strategy to decrease illicit opioid use or to increase retention in methadone maintenance therapy among patients with opioid use disorder.