Variations in the protective association between opioid agonist therapy and opioid overdose death by age and chronic disease status: findings from the OATS retrospective linked data study, NSW, Australia, 2001-2018.

Background: Opioid agonist treatment (OAT) is strongly protective against overdose and all-cause mortality. In many countries, the OAT population is aging, with concomitant increases in systemic diseases that are associated with increased overdose risk. We tested whether OAT is as protective against overdose death for older and more comorbid people with opioid use disorder, compared to their counterparts.

Methods: The sample included all people receiving OAT in New South Wales, Australia, between 2001 and 2018, with linkage of OAT data to mortality and hospitalisation records. Opioid overdose deaths and hospitalisations for chronic respiratory, circulatory, kidney, and liver diseases were defined using ICD-10 codes. We developed generalised estimating equation models comparing opioid overdose mortality rates during treatment between different age groups and in people with and without each category of chronic disease.

Results: There were 420,410 person-years (py) of observation, and 1,279 opioid overdose deaths. Opioid overdose mortality rates during OAT were higher in older age groups (e.g. over 50 years: 1.7 (95% CI: 1.4, 2.1) deaths per 1000 py; under 30 years: 0.6 (95% CI: 0.4, 0.8) deaths per 1000 py). The relative risk of overdose death while in OAT among those aged under 30 years was one-third that of those aged over 50 years (adjusted RR 0.32; 95% CI 0.17, 0.61). Opioid overdose mortality rates during OAT were significantly elevated among people with each of the specified chronic diseases, relative to those without these diagnoses.

Discussion: OAT may not confer the same level of protection against opioid overdose death among clients aged over 50 and/or with chronic diseases, and targeted interventions may be required to address their overdose risk. Improved access to primary care may support better health in older people with opioid use disorder.