Efficacy of cocaine contingency management in heroin-assisted treatment: Results of a randomized controlled trial

AIMS: To determine the efficacy of contingency management (CM), targeting cocaine use, as an add-on intervention for heroin dependent patients in supervised heroin-assisted treatment (HAT) with frequent cocaine use.

DESIGN: Multi-center, open-label, parallel group, randomized controlled trial.

SETTING: Twelve specialized addiction treatment centers for HAT in The Netherlands; April 2006-January 2011.

PARTICIPANTS: 214 chronic, treatment-refractory heroin dependent patients in HAT, with frequent cocaine use.

INTERVENTIONS: Routine, daily supervised diacetylmorphine treatment, co-prescribed with oral methadone (HAT), with and without 6 months contingency management for cocaine use as an add-on intervention; HAT+CM and HAT-only, respectively.

MEASUREMENTS: Primary outcome was the longest, uninterrupted duration of cocaine abstinence, based upon laboratory urinalysis. Secondary outcome measures included other cocaine-related measures, treatment retention in HAT, and multi-domain health-related treatment response.

FINDINGS: In an intention-to-treat analysis, HAT+CM was more effective than HAT-only in promoting longer, uninterrupted duration of cocaine abstinence (3.7 weeks versus 1.6 weeks; negative binomial regression: Exp(B)=2.34, 95%-CI: 1.70-3.23; p<0.001). This result remained significant in sensitivity analyses and was supported by all secondary, cocaine-related outcome measures. Treatment retention in HAT was high (91.6%) with no difference between the groups. The improvement in multi-domain health-related treatment response during the trial was numerically higher in HAT+CM (from 37.4% to 53.1%; +15.7%) than in HAT-only (from 44.5% to 46.5%; +2.0%), but this difference was statistically not significant.

CONCLUSIONS: Contingency management is an effective add-on intervention to promote longer, uninterrupted periods of cocaine abstinence in chronic, treatment-refractory heroin dependent patients in heroin-assisted treatment with frequent cocaine use. The trial has been registered in The Netherlands National Trial Register under clinical trial registration number NTR4728.