Characteristics of adherence to methadone maintenance treatment over a 15-year period among homeless adults experiencing mental illness

Background Methadone maintenance treatment (MMT) has important protective effects related to reduced illicit opioid use, infectious disease transmission, and overdose mortality. Adherence to MMT has not been examined among homeless people. We measured MMT adherence and reported relevant characteristics among homeless adults experiencing mental illness in Vancouver, British Columbia, Canada. Material and methods Homeless adults living with mental illness who had received MMT prior to the baseline interview of the Vancouver At Home study (n = 78) were included in analyses. The medication possession ratio (MPR) was used to estimate MMT adherence from retrospective administrative pharmacy and public health insurance data collected across 15 years. Independent sample t tests and one-way ANOVA were used to test for significant differences in MMT MPR by participant characteristics. Results Mean MMT MPR was 0.47. A large proportion of participants reported blood-borne infectious disease, three or more chronic physical health conditions, and substance use. Being single and never married was associated with significantly lower MMT MPR (0.40 vs. 0.55, p = 0.036), while living with schizophrenia, bipolar disorder, or a mood disorder with psychotic features was associated with significantly higher MMT MPR (0.54 vs. 0.37, p = 0.022). Daily drug use (excluding alcohol) was associated with significantly lower MMT MPR (0.39 vs. 0.54, p = 0.051). Conclusions The level of adherence to MMT was very low among homeless adults experiencing mental illness. Efforts are needed to improve adherence to MMT as a means of reducing illicit substance use, preventing overdose deaths, and attenuating infectious disease transmission.