Impact of baseline methamphetamine/amphetamine use on discontinuation of methadone and buprenorphine/naloxone among people with prescription-type opioid use disorder in Canada.

Background And Objectives: Although concurrent stimulant use is common among people with opioid use disorder (OUD), there is little evidence on its impacts on opioid agonist therapy (OAT) outcomes. This study sought to determine the impact of baseline methamphetamine/amphetamine use on discontinuation of OAT among individuals with prescription-type OUD (POUD) initiating methadone or buprenorphine/naloxone as part of a pragmatic randomized trial in Canada.

Methods: Secondary analysis of a pan-Canadian pragmatic trial conducted between 2017 and 2020 comparing supervised methadone versus flexible take-home dosing buprenorphine/naloxone models of care. Cox proportional hazard models were used to evaluate the effect of baseline methamphetamine/amphetamine use (measured by urine drug test [UDT]) on two discontinuation outcomes (i.e., assigned OAT discontinuation, any OAT discontinuation).

Results: Two hundred nine (n = 209) participants initiated OAT, of which 96 (45.9%) had positive baseline methamphetamine/amphetamine UDT. Baseline methamphetamine/amphetamine use was associated with shorter median times in assigned OAT (21 vs. 168 days, hazard ratio [aHR] = 2.45, 95% confidence interval [CI] = 1.60-3.76) and any OAT (25 days vs. 168 days, aHR = 2.06, CI = 1.32-3.24). No interaction between methamphetamine/amphetamine and assigned OAT was observed for either outcome (p > .05).

Conclusion And Scientific Significance: This study offers novel insights on the impact of methamphetamine/amphetamine use on OAT outcomes among people with POUD. Methamphetamine/amphetamine use was common and was associated with increased risk of OAT discontinuation. Supplementary interventions, including treatment for stimulant use, are needed to improve retention in OAT and optimize treatment outcomes in this population.