Factors associated with discontinuation of methadone maintenance therapy (MMT) among persons who also use alcohol in Vancouver, Canada

Background
We sought to examine the factors associated with discontinuation of MMT among persons on methadone who use alcohol.
Methods
We evaluated the impact of drug-related and other factors on discontinuation of MMT among persons enrolled in MMT and who reported any use of alcohol versus those who were enrolled in two community-recruited prospective cohorts of people who use illicit drugs (PWUD). Extended Cox models with time-dependent variables identified factors independently associated with time to first MMT discontinuation.
Results
Between December 2005 and 2015, 823 individuals on MMT who also reported using alcohol at least once were included in these analyses. During the study period, 391 (47.5%) discontinued methadone. Daily heroin injection (Adjusted Hazard Ratio [AHR] = 2.67, 95% Confidence Interval [CI]: 2.10–3.40) and homelessness (AHR = 1.42, 95% CI: 1.10–1.83) were positively associated with MMT discontinuation, whereas receiving other concurrent addiction treatment in addition to MMT (AHR = 0.07, 95% CI: 0.05–0.08), as well as >60 mg methadone dose (AHR = 0.48, 95% CI: 0.39–0.60), Hepatitis C virus seropositivity (AHR = 0.65, 95% CI: 0.47–0.90), and HIV seropositivity (AHR = 0.72, 95% CI: 0.57–0.91) were negatively associated with MMT discontinuation. Any/heavy alcohol use was not independently associated with MMT discontinuation.
Conclusions
This study reinforces the known risks of continued heroin injection and homelessness for MMT discontinuation among individuals who also consume alcohol and highlights the protective effect of both MMT dose and receipt of concurrent addiction treatment.