Modeling the population‐level impact of opioid agonist treatment on mortality among people accessing treatment between 2001 and 2020 in New South Wales, Australia

BACKGROUND AND AIMS: The individual‐level effectiveness of opioid agonist treatment (OAT) in reducing mortality is well established, but there is less evidence on population‐level benefits. We use modeling informed with linked data from the OAT program in New South Wales (NSW), Australia, to estimate the impact of OAT provision in the community and prisons on mortality and the impact of eliminating excess mortality during OAT initiation/discontinuation. DESIGN: Dynamic modeling. SETTING AND PARTICIPANTS: A cohort of 49 359 individuals who ever received OAT in NSW from 2001 to 2018. MEASUREMENTS: Receipt of OAT was represented through five stages: (i) first month on OAT, (ii) short (1–9 months) and (iii) longer (9+ months) duration on OAT, (iv) first month following OAT discontinuation and (v) rest of time following OAT discontinuation. Incarceration was represented as four strata: (i) never or not incarcerated in the past year, (ii) currently incarcerated, (iii) released from prison within the past month and (iv) released from prison 1–12 months ago. The model incorporated elevated mortality post‐release from prison and OAT impact on reducing mortality and incarceration. FINDINGS: Among the cohort, mortality was 0.9 per 100 person‐years, OAT coverage and retention remained high (> 50%, 1.74 years/episode). During 2001–20, we estimate that OAT provision reduced overdose and other cause mortality among the cohort by 52.8% [95% credible interval (CrI) = 49.4–56.9%] and 26.6% (95% CrI =22.1–30.5%), respectively. We estimate 1.2 deaths averted and 9.7 life‐years gained per 100 person‐years on OAT. Prison OAT with post‐release OAT‐linkage accounted for 12.4% (95% CrI = 11.5–13.5%) of all deaths averted by the OAT program, primarily through preventing deaths in the first month post‐release. Preventing elevated mortality during OAT initiation and discontinuation could have averted up to 1.4% (95% CrI = 0.8–2.0%) and 3.0% (95% CrI = 2.1–5.3%) of deaths, respectively. CONCLUSION: The community and prison opioid agonist treatment program in New South Wales, Australia appears to have substantially reduced population‐level overdose and all‐cause mortality in the past 20 years, partially due to high retention.