Randomized trial of prize-based reinforcement density for simultaneous abstinence from cocaine and heroin

Abstract

To examine the effect of reinforcer density in prize-based abstinence reinforcement, heroin/cocaine users (N = 116) in methadone maintenance (100 mg/day) were randomly assigned to a noncontingent control group (NonC) or to 1 of 3 groups that earned prize draws for abstinence: manual drawing with standard prize density (MS) or computerized drawing with standard (CS) or high (CH) density. Probabilities (prizes/draw) were standard (50%) and high (78%); prize density was double blind. Mean prize values were CH, $286; CS, $167; MS, $139; and NonC, $171. Outcomes were % opioid/cocaine-negative urines during the 12-week intervention and then 8 weeks postintervention as well as diagnosis of dependence up to 6 months poststudy. CH had significantly more negative specimens than did NonC during intervention and had more than all groups during postintervention treatment: Mean % negative (95% confidence interval) during postintervention treatment adjusted for baseline drug use and dropout were CH, 55% (14%-90%); CS, 7% (1%-27%); MS, 4% (1%-12%); and NonC, 3% (1%-10%). Current cocaine dependence diagnoses after treatment were significantly lower in contingent compared with noncontingent groups. Computerized drawing with higher-density prizes enhanced reduction of cocaine use; abstinence reinforcement had long-term therapeutic benefits.

(PsycINFO Database Record (c) 2007 APA, all rights reserved).

Figures

Figure 1

CONSORT flowchart of participants’ progress through the study.

Figure 2

A: Mean raw percentages of urine specimens by treatment group that were negative from both cocaine and opiate use in the baseline phase (first 5 weeks), prize-drawing intervention phase (next 12 weeks), and maintenance/posttreatment (return-to-baseline) phase (final 8 weeks). The seeming group difference in baseline drug use is not statistically significant but is controlled for in the adjusted percentages shown in Panel B. B: Adjusted percentages of urine specimens by treatment group that were negative from both cocaine and opiate use in the prize-drawing intervention phase (12 weeks), and maintenance/posttreatment (return-to-baseline) phase (final 8 weeks). Each adjusted percentage is a μ value from a random-effects mixed-regression model (SAS GLIMMIX macro) controlling for baseline drug use—expressed as (a) the percentage of urine specimens negative for both opiates and cocaine, arcsine transformed; (b) negative for cocaine, arcsine transformed; and (c) negative for opiates, arcsine transformed—and for treatment duration (continuous variable: the number of the last urine specimen collected during the maintenance/postintervention phase of the study).