Does exposure to opioid substitution treatment in prison reduce the risk of death after release? A national prospective observational study in England.

BACKGROUND AND AIMS People with opioid use disorder (OUD) in prison face an acute risk of death after release. We estimated whether prison-based opioid substitution treatment (OST) reduces this risk. DESIGN Prospective observational cohort study using prison health care, national community drug misuse treatment and deaths registers. SETTING Recruitment at 39 adult prisons in England (32 male; seven female) accounting for 95% of OST treatment in England during study planning. PARTICIPANTS Adult prisoners diagnosed with OUD (recruited: September 2010-August 2013; first release: September 2010; last release: October 2014; follow-up to February 2016; n = 15 141 in the risk set). INTERVENTION AND COMPARATOR At release, participants were classified as OST exposed (n = 8645) or OST unexposed (n = 6496). The OST unexposed group did not receive OST, or had been withdrawn, or had a low dose. MEASUREMENTS Primary outcome: all-cause mortality (ACM) in the first 4 weeks. SECONDARY OUTCOMES drug-related poisoning (DRP) deaths in the first 4 weeks; ACM and DRP mortality after 4 weeks to 1 year; admission to community drug misuse treatment in the first 4 weeks. Unadjusted and adjusted Cox regression models (covariates: sex, age, drug injecting, problem alcohol use, use of benzodiazepines, cocaine, prison transfer and admission to community treatment), tested difference in mortality rates and community treatment uptake. FINDINGS During the first 4 weeks after prison release there were 24 ACM deaths: six in the OST exposed group and 18 in the OST unexposed group [mortality rate 0.93 per 100 person-years (py) versus 3.67 per 100 py; hazard ratio (HR) = 0.25; 95% confidence interval (CI) = 0.10-0.64]. There were 18 DRP deaths: OST exposed group mortality rate 0.47 per 100 py versus 3.06 per 100 py in the OST unexposed group (HR = 0.15; 95% CI = 0.04-0.53). There was no group difference in mortality risk after the first month. The OST exposed group was more likely to enter drug misuse treatment in the first month post-release (odds ratio 2.47, 95% CI = 2.31-2.65). The OST mortality protective effect on ACM and DRP mortality risk was not attenuated by demographic, overdose risk factors, prison transfer or community treatment (fully adjusted HR = 0.25; 95% CI = 0.09-0.64 and HR = 0.15; 95% CI = 0.04-0.52, respectively). CONCLUSIONS In an English national study, prison-based opioid substitution therapy was associated with a 75% reduction in all-cause mortality and an 85% reduction in fatal drug-related poisoning in the first month after release.