Effects of incentives for naltrexone adherence on opiate abstinence in heroin-dependent adults

Aim To test whether an incentive-based intervention that increased adherence to naltrexone also increased opiate abstinence. Design Post-hoc combined analysis of three earlier randomized controlled trials that showed individually that incentives for adherence to oral and to extended-release injection naltrexone dosing schedules increased naltrexone adherence, but not opiate abstinence. Setting Out-patient therapeutic work-place in Baltimore, MD, USA. Participants One hundred and forty unemployed heroin-dependent adults participating from 2006 to 2010. Interventions Participants were hired in a model work-place for 26 weeks and randomized to a contingency (n = 72) or prescription (n = 68) group. Both groups were offered naltrexone. Contingency participants were required to take scheduled doses of naltrexone in order to work and earn wages. Prescription participants could earn wages independent of naltrexone adherence. Measures Thrice-weekly and monthly urine samples tested for opiates and cocaine and measures of naltrexone adherence (percentage of monthly urine samples positive for naltrexone or percentage of scheduled injections received). All analyses included pre-randomization attendance, opiate use and cocaine use as covariates. Additional analyses controlled for cocaine use and naltrexone adherence during the intervention. Findings Contingency participants had more opiate abstinence than prescription participants (68.1 versus 52.9% opiate-negative thrice-weekly urine samples, respectively; and 71.9 versus 61.7% opiate-negative monthly urine samples, respectively) based on initial analyses [thrice-weekly samples, odds ratio (OR) = 3.3, 95% confidence interval (CI) = 1.7–6.5, P