Opioid agonist therapy engagement and crystal methamphetamine use: The impact of unregulated opioid use in Vancouver, Canada.

backgroundCrystal methamphetamine use has substantially increased among people who use opioids in recent years, yet the impact of opioid agonist therapy (OAT) on crystal methamphetamine use remains poorly characterized. Therefore, we sought to examine the relationship between OAT engagement and crystal methamphetamine use and to assess if this relationship differs according to the ongoing use of unregulated opioids.

methodsData was collected from two harmonized ongoing prospective cohorts of people who use drugs in Vancouver, Canada, between December 2005 and March 2020. We employed multivariable generalized estimating equations to study the relationship between OAT engagement and crystal meth use stratified by ongoing unregulated opioid use.

resultsOf 1742 participants who reported frequent opioid use at baseline, the median age was 42 years, and 61.3% were male. Multivariable analyses showed that compared to those who had not received OAT for at least one year: in the absence of ongoing unregulated opioid use, individuals who recently discontinued (adjusted Odds Ratio [aOR] = 0.47, 95% CI = 0.27-0.79), newly initiated (aOR = 0.52, 95% CI = 0.31-0.89), or were retained on OAT (aOR = 0.48, 95% CI = 0.31-0.72) reported a lower frequency of crystal methamphetamine use; in the presence of ongoing unregulated opioid use, individuals who newly initiated OAT reported a greater crystal methamphetamine use frequency (aOR = 1.24, 95% CI = 1.02-1.51).

conclusionsWe demonstrated a differential relationship between OAT engagement and crystal methamphetamine use that was conditional on the ongoing use of unregulated opioids. Our findings highlight the complexity of OAT implementation and suggest that polysubstance use patterns should be an important consideration for care providers when devising comprehensive treatment strategies and prognosticating treatment effects.