Opioid overdose risk during and after drug treatment for heroin dependence: An incidence density case–control study nested in the VEdeTTE cohort

INTRODUCTION AND AIMS To corroborate protective effects of a range of drug treatment modalities against overdose mortality risk. DESIGN AND METHODS Nested case-control study, with incidence density sampling, selecting controls retrospectively at each case event. Cases and controls came from a sub-cohort of opioid-dependent patients (n = 4444) from two Italian regions (Lazio and Piedmont). From 1998 to 2005, there were 91 overdose deaths (cases) matched to 352 controls. The primary outcome was overdose mortality and the primary exposure was drug treatment: opioid agonist treatment (OAT), opioid detoxification, residential community, psychosocial and other pharmacological treatment. Conditional logistic regression models generated intervention effects comparing mortality risk in and out of treatment, adjusting for confounding variables. RESULTS Overall, drug treatment reduced overdose mortality risk by 80% [adjusted odds ratio (AOR) 0.18, 95% confidence interval (CI) 0.10-0.33, P