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 individually showed that incentives for adherence to oral and to extended-release injection naltrexone dosing schedules increased naltrexone adherence but not opiate abstinence.
Setting
Outpatient therapeutic workplace in Baltimore, MD, USA.
Participants
140 unemployed heroin-dependent adults participating from 2006–2010.
Interventions
Participants were hired in a model workplace 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 prerandomization 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% vs. 52.9% opiate-negative thrice-weekly urine samples, respectively; and 71.9% vs. 61.7% opiate-negative monthly urine samples, respectively) based on initial analyses (thrice-weekly samples, OR = 3.3, 95% CI = 1.7–6.5, p < .01; monthly samples, OR = 2.6, 95% CI = 1.0–7.1, p = .06) and on analyses that controlled for cocaine use (thrice-weekly samples, OR = 3.9, 95% CI = 3.3–4.5, p < .01; monthly samples, OR = 3.4, 95% CI = 1.1–11.1, p =.04), which was high and associated with opiate use. The difference in opiate abstinence rates between Contingency participants and Prescription participants was reduced when controlling for naltrexone adherence (monthly samples, OR = 1.1, 95% CI = 0.7–1.7, p = .84).
Conclusions
Incentives for naltrexone adherence increase opiate abstinence in heroin-dependent adults, an effect that appears to be due to increased naltrexone adherence produced by the incentives.