Factors associated with methadone maintenance therapy discontinuation among people who inject drugs

Methadone maintenance therapy (MMT) continues to be a key treatment for opioid use disorder, although premature discontinuation of MMT can increase risk for overdose and other severe harms. We examined sociodemographic characteristics, substance use patterns and social-structural exposures associated with MMT discontinuation among a cohort of people who use drugs (PWUD) in Vancouver, Canada.

Data were derived from VIDUS and ACCESS, prospective cohorts of PWUD in Vancouver, Canada. The outcome of interest was self-reported discontinuation of MMT within the last six months. Multivariable Generalized Estimating Equations (GEE) were conducted to identify factors independently associated with MMT discontinuation.

Between 2005 and 2015, 1301 PWUD who had accessed MMT were recruited, among whom 288 (22.1%) discontinued MMT at least once during the study period. In multivariable GEE analyses, homelessness (Adjusted Odds Ratio [AOR] = 1.46, 95% Confidence Interval [95% CI]: 1.09-1.95), daily heroin injection (AOR = 5.17, 95% CI: 3.82-6.99), daily prescription opioid use (injection or non-injection) (AOR = 2.18, 95% CI: 1.30-3.67), recent incarceration (AOR = 1.46, 95% CI: 1.01-2.12), and not being on any form of income assistance (AOR = 2.14, 95% CI: 1.33-3.46) were each independently positively associated with MMT discontinuation. Participants with more study visits on methadone (>50% vs. ≤50% of visits) (AOR = 0.63, 95% CI: 0.47-0.85) and those with higher methadone dose (>100 mg vs. <60 mg per day) (AOR = 0.44, 95% CI: 0.31-0.62) were less likely to discontinue MMT.

Discontinuation of MMT in this urban setting was associated with recent homelessness and incarceration, not accessing social income assistance, as well as daily prescription opioid use and daily heroin injection drug use. These findings underscore a need to reduce potential barriers to MMT retention by providing access to stable housing and preventing treatment interruptions during transitions between community and custodial settings.