Incidence of suicide and self-harm among people with opioid use disorder and the impact of opioid agonist treatment: A retrospective data linkage study

Background: Rates of suicide and self-harm are elevated among people with opioid use disorder (OUD). This study examined incidence of self-harm and suicide among people who have entered OAT and assessed the impact of different OAT exposure periods on these events. Method: We conducted a retrospective population-based cohort study of all OAT recipients (N = 45,664) in New South Wales, Australia (2002-2017), using linked administrative data. Incidence rates of self-harm hospitalisations and suicide deaths were estimated per 1000 person-years (PY). The first 28 days of an OAT episode, >= 29 days on OAT, the first 28 days off OAT, and >= 29 days off OAT (maximum four years post-OAT) were exposure periods. Poisson regression models with generalised estimating equations estimated the adjusted incidence rate ratios (ARR) of self-harm and suicide by OAT exposure periods, adjusting for covariates. Results: There were 7482 hospitalisations (4148 individuals) for self-harm and 556 suicides, equating to incidence rates of 19.2 (95% confidence intervals [CI]=18.8-19.7) and 1.0 (95%CI=0.9-1.1) per 1000 PY, respectively. Opioid overdose was implicated in 9.6% of suicides and 28% of self-harm hospitalisations. Compared to >= 29 days on OAT, the incidence rate of suicide was elevated in the 28 days following OAT cessation (ARR=17.4 [95%CI=11.7-25.9]), and the rate of self-harm hospitalisations was elevated during the first 28 days of OAT (ARR=2.2 [95%CI=1.9-2.6]) and the 28 days after leaving OAT (ARR=2.7 [95% CI=2.3-3.2]). Conclusions: OAT may reduce suicide and self-harm risk among people with OUD; however, OAT initiation and cessation are critical periods for targeting self-harm and suicide prevention interventions.