Retention in opioid agonist therapy among First Nations people in Ontario, Canada: a retrospective cohort study

Importance — First Nations people are disproportionately impacted by the opioid crisis in Canada. While many First Nation communities have expanded access to treatment, there is a need to better understand the factors associated with early discontinuation of opioid agonist therapies (OAT).

Objective — To investigate factors associated with OAT retention within the first year of treatment among First Nations people in Ontario, Canada.

Design, setting, and participants — This was a population-based retrospective cohort study including all registered (status) First Nations people aged 15 years or older initiating OAT between January 2013 and March 2021. Data were analyzed between October 2022 and June 2024.

Exposure — Methadone and buprenorphine-naloxone initiation.

Main outcomes and measures — The main outcome was duration of OAT treatment, with discontinuation defined as a gap in therapy of more than 14 days. Cox proportional hazards models followed up individuals until the first occurrence of OAT discontinuation, death, end of 1-year follow-up, or switching between OAT treatments.

Results — A total of 17 880 OAT initiations among 7476 individuals (median [IQR] age, 31 [26-38] years; 8966 [50.1%] female) were identified, including 9074 new episodes of buprenorphine-naloxone and 8806 new episodes of methadone. Time to treatment discontinuation was shorter among buprenorphine-naloxone episodes (median [IQR], 42 [5-321] days) compared with methadone episodes (median [IQR], 71 [10-544] days) (P < .001). Several factors were associated with buprenorphine-naloxone and methadone retention, including living in moderately sized urban areas (buprenorphine-naloxone: adjusted hazard ratio [aHR], 0.81; 95% CI, 0.70-0.95; methadone: aHR, 0.79; 95% CI, 0.70-0.90) and being recently dispensed non-OAT opioids (buprenorphine-naloxone: aHR, 0.86; 95% CI, 0.80-0.94; methadone: aHR, 0.86; 95% CI, 0.79-0.93). In contrast, factors associated with higher rates of discontinuation included recent opioid toxic events (buprenorphine-naloxone: aHR, 1.36; 95% CI, 1.20-1.54; methadone: aHR, 1.24; 95% CI, 1.11-1.38), and recent methadone treatment (buprenorphine-naloxone: aHR, 1.09; 95% CI, 1.01-1.18; methadone: aHR, 1.67; 95% CI, 1.57-1.78). Methadone discontinuation increased over time; however this pattern was not observed for buprenorphine-naloxone.

Conclusions and relevance — This cohort study among First Nations people found low rates of OAT retention. Although retention was higher for methadone, it declined over time. These findings highlights important gaps in OAT provision for First Nations people that may be improved by investments into First Nations–led treatment programs that integrate traditional, land-based programs to better support people with opioid use disorder across Ontario.