Cannabis Use and Methadone Maintenance Treatment Outcomes in Patients with Opioid Use Disorder

Abstract

Background: Methadone maintenance treatment (MMT) is a commonly prescribed therapy for patients with opioid use disorder, yet inter-individual variability in terms of treatment response is evident. Given the high prevalence of cannabis use in this population, this thesis aims to elucidate the association between cannabis use and MMT outcomes. Methods: We conducted a systematic review and meta-analysis to comprehensively evaluate the literature and quality of evidence, as well as to identify gaps in the literature to inform future research. We then conducted a cross-sectional study investigating sex differences in the association between cannabis use and illicit opioid use in MMT patients. We employed a multivariable logistic regression analysis to assess the influence of any cannabis use as well as heaviness of cannabis use within men and women. Results: The systematic review included 22 observational studies. Results revealed the low quality of available evidence as well as substantial heterogeneity among studies. We identified several limitations in the evidence base including reliance on crude measures of cannabis use and inadequate consideration of confounding variables. Our cross-sectional study included a sample of 777 patients on MMT. Consistent with previous research, we found cannabis use to be unrelated to illicit opioid use in the entire sample. However when we stratified the analysis by sex, we found cannabis use was associated with increased odds of having concurrent illicit opioid use. Conclusion: Results of this thesis suggest certain populations within MMT patients may be at higher risk of experiencing adverse effects of cannabis in terms of treatment outcomes. Future work can build on the results of these studies to identify unique risk factors for patients in order to inform the use of tailored treatment options to improve MMT effectiveness.