UBC Theses and Dissertations
Polysubstance use patterns among people with opioid use disorder in Vancouver, Canada Karamouzian, Mohammad
Background: A growing body of evidence suggests that people with opioid use disorder (OUD) engage in polysubstance use (PSU). However, most studies are variable-centred and cross-sectional, and as a result, several aspects of longitudinal PSU patterns amongst people with OUD remain understudied. This thesis investigated longitudinal PSU classes among people with OUD by pursuing these specific objectives: systematically review the evidence on PSU classes among people with OUD; describe people with OUD’s substance use patterns after a national supply-level reduction intervention (i.e., reformulation of OxyContin); identify person-centred longitudinal patterns of PSU among them; and assess the longitudinal association between membership in different classes of PSU and non-fatal overdose events. Methods: To summarize the literature on PSU amongst people with OUD, a literature search was conducted following standard systematic review guidelines. Empirical data were obtained from three prospective cohorts of people who use drugs in Vancouver, Canada. Interrupted time-series (ITS) analysis was used to assess how people with OUD’s substance use patterns changed after the reformulation of OxyContin in Canada. Repeated measures latent class analysis (RMLCA) and longitudinal multivariable generalized estimating equations models were applied to identify distinct longitudinal classes of PSU and their associated odds of non-fatal overdose. Results: The systematic review identified 30 eligible studies and documented numerous PSU patterns among people with OUD and several methodological limitations in the literature. The ITS analysis showed that reducing access to OxyContin was not associated with reductions in illicit opioid use among people with OUD. The RMLCA analysis found five distinct longitudinal PSU patterns, including low/infrequent use, primarily opioid and methamphetamine use, primarily cannabis use, primarily opioid and crack use, and persistent PSU. Those in higher-intensity PSU classes were at higher odds of non-fatal overdose. Conclusion: This research underscored the heterogeneous nature of people with OUD in terms of both longitudinal substance use patterns and long-term odds for non-fatal overdose. It also highlighted the limited capacity of supply-level interventions in reducing opioid use among people with OUD. The high frequency of polysubstance use and heterogeneities among people with OUD should be reflected in OUD-related research, policy, and clinical practice developments.
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