Impact of treatment for opioid dependence on fatal drug-related poisoning: A national cohort study in England

Abstract

Aims: To compare the change in illicit opioid users' risk of fatal drug-related poisoning (DRP) associated with opioid agonist pharmacotherapy (OAP) and psychological support, and investigate the modifying effect of patient characteristics, criminal justice system (CJS) referral and treatment completion. Design: National data linkage cohort study of the English National Drug Treatment Monitoring System and the Office for National Statistics national mortality database. Data were analysed using survival methods. Setting: All services in England that provide publicly funded, structured treatment for illicit opioid users. Participants: Adults treated for opioid dependence during April 2005 to March 2009: 151983 individuals; 69% male; median age 32.6 with 442950 person-years of observation. Measurements: The outcome was fatal DRP occurring during periods in or out of treatment, with adjustment for age, gender, substances used, injecting status and CJS referral. Findings: There were 1499 DRP deaths [3.4 per 1000 person-years, 95% confidence interval (CI)=3.2-3.6]. DRP risk increased while patients were not enrolled in any treatment [adjusted hazard ratio (aHR)=1.73, 95% CI=1.55-1.92]. Risk when enrolled only in a psychological intervention was double that during OAP (aHR=2.07, 95% CI=1.75-2.46). The increased risk when out of treatment was greater for men (aHR=1.88, 95% CI=1.67-2.12), illicit drug injectors (aHR=2.27, 95% CI=1.97-2.62) and those reporting problematic alcohol use (aHR=2.37, 95% CI=1.90-2.98). Conclusions: Patients who received only psychological support for opioid dependence in England appear to be at greater risk of fatal opioid poisoning than those who received opioid agonist pharmacotherapy.