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UBC Theses and Dissertations

Substance use trajectories and impacts of drug treatment among people who use illicit drugs in Vancouver, Canada Dong, Huiru


Background: The opioid overdose epidemic represents an unprecedented public health crisis in North America. Scientific evidence concerning long-term substance use trajectories and their impact on treatment outcomes among people who use drugs (PWUD) is critical to informing efforts designed to mitigate the harms of opioid dependency. This dissertation sought to: 1) identify factors promoting opioid use cessation among people receiving opioid agonist therapy (OAT); 2) characterize long-term injection drug use trajectories among PWUD; and 3) examine how pre- treatment opioid use patterns affect OAT outcomes as well as the impact of OAT on patterns of polysubstance use. Methods: Data for Chapter 2 came from a systematic review of research published between 1996 and 2019. Data for Chapters 3-5 were derived from three community-based prospective cohort studies of PWUD in Vancouver, Canada. Longitudinal analytical techniques were utilized, including: growth mixture model and multinomial logistic regression (Chapter 3); latent class growth analysis and generalized linear mixed-effects model (Chapter 4); and segmented regression (Chapter 5). Results: Findings from the systematic review demonstrated that among people receiving OAT, additional psychosocial interventions could help promote opioid cessation. In Chapter 3, five injection drug use trajectories were identified, ranging from persistent high-frequency use to early cessation. These trajectories were associated with baseline individual characteristics and drug use behaviours. In Chapter 4, two pre-treatment opioid use classes were identified (i.e., high frequency users and gradually increasing frequency users), which were related to subsequent treatment outcomes. In Chapter 5, a significant reduction in illicit opioid use was observed following OAT initiation. There was no significant difference comparing the pre-treatment and post-treatment trends for stimulants and cannabis. However, increasing problematic alcohol use was noted during the post-treatment period. Conclusion: There is a high level of heterogeneity in long-term substance use trajectories. The impact of treatment varies as a function of these substance use trajectories, individual characteristics, and the complex social and environmental contexts in which PWUD live. The findings reiterate the importance of developing long-term treatment strategies for people with substance use disorder and implementing services tailored to the needs of individuals characterized by distinct substance use trajectories.

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