Cause-Specific Mortality among Patients in Treatment for Opioid Use Disorder in Multiple Settings: A Prospective Comparative Cohort Study

Introduction: Among people receiving current or previous opioid maintenance treatment (OMT), the leading cause of premature death is an opioid overdose. However, other causes of mortality remain high in this group. An understanding of causes of deaths across multiple settings can be useful in informing more comprehensive prevention responses. The aim of this study was to describe all non-overdose causes of death in three national cohorts (Czechia, Denmark, and Norway) among OMT patients and to explore associations of non-overdose mortality with age and gender. Methods: This prospective comparative cohort study used national mortality registry databases for OMT patients from Czechia (2000-2019), Denmark (2000-2018), and Norway (2010-2019). Crude mortality rates and age-standardized mortality rates (ASMRs) were calculated as deaths per 1,000 person years for cause-specific mortality. Results: In total, 29,486 patients were included, with 5,322 deaths recorded (18%). We found variations in causes of death among the cohorts and within gender and age groups. The leading non-overdose causes of death were accidents in Czechia and Denmark, and neoplasms in Norway. Cardiovascular deaths were highest in Czechia, particularly for women in OMT (ASMR 3.59 vs. 1.24 in Norway and 1.87 in Denmark). Conclusion: This study found high rates of preventable death among both genders and all age groups. Different demographic structures, variations in risk exposure, as well as variations in coding practices can explain the differences. The findings support increased efforts towards screening and preventative health initiatives among OMT patients specific to the demographic characteristics in different settings.