UBC Theses and Dissertations
Methamphetamine use among people who use opioids : longitudinal patterns and the role of opioid agonist therapy Cui, Zishan
Background: Methamphetamine use is on the rise among people who use opioids (PWUO), which brings additional complexity to the landscape of opioid agonist therapy (OAT). However, the circumstances surrounding methamphetamine use among PWUO and the role of OAT in this context remain under-explored. The overarching aims of this dissertation were to: 1) understand the social context surrounding methamphetamine use among PWUO and 2) explore the interplay between methamphetamine use and OAT among PWUO. Methods: I first conducted a systematic review to synthesize the studies characterizing the trend of and factors associated with methamphetamine use among PWUO. Then, using empirical data obtained from two prospective cohorts of people who use drugs in Vancouver, Canada, between 2005 and 2020, I conducted multivariable generalized estimating equation (GEE) analyses to identify predictors of methamphetamine use initiation among individuals on OAT and examine the relationship between OAT engagement and methamphetamine use frequency among PWUO. Last, I employed repeated measures latent class analysis (RMLCA) to identify longitudinal substance use patterns among people receiving OAT, and used marginal structural Cox modeling to estimate their association with OAT discontinuation. Results: The systematic review found a wide range of individual, microsocial, and macrosocial factors associated with methamphetamine use among PWUO. The multivariable GEE analyses identified factors associated with methamphetamine initiation among individuals on OAT, including younger age, unstable housing, unprotected sex, previous methamphetamine use, recent cocaine use, and recent non-medical opioid use. Among PWUO, OAT engagement was associated with a lower methamphetamine use frequency in the absence of ongoing non-medical opioid use, while OAT initiation was associated with a greater methamphetamine use frequency. The RMLCA analysis identified four distinct substance use classes among people receiving OAT, with the opioid and stimulant use classes exhibiting a higher risk of OAT discontinuation. Conclusion: Addressing the ongoing overdose crisis requires comprehensive strategies encompassing prevention, intervention, and harm reduction efforts that consider both opioid and methamphetamine use. Care providers should adopt person-centred treatment approaches to meet the individualized needs of patients. Future research is needed to actively explore integrated treatment approaches and develop effective pharmaceutical interventions targeting concurrent opioid and methamphetamine use.
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