Randomized clinical trial examining duration of voucher-based reinforcement therapy for cocaine abstinence

Abstract

Background: This is the first study to systematically manipulate duration of voucher-based reinforcement therapy (VBRT) to see if extending the duration increases abstinence during and following VBRT.

Methods: We randomized cocaine-dependent methadone-maintained adults to Standard (12 weeks; n=62) or Extended (36 weeks; n=68) VBRT and provided escalating voucher amounts contingent upon urinalysis verification of cocaine abstinence. Urinalysis was scheduled at least every 2 weeks during the 48-week study and more frequently during VBRT (3/week) and 12 weeks of Aftercare (2/week).

Results: Extended VBRT produced longer durations of continuous cocaine abstinence during weeks 1-24 (5.7 vs 2.7 weeks; p=0.003) and proportionally more abstinence during weeks 24-36 (X(2)=4.57, p=.03, OR=2.18) compared to Standard VBRT. Duration of VBRT did not directly predict after-VBRT abstinence; but longer continuous abstinence during VBRT predicted abstinence during Aftercare (p=0.001) and during the last 12 weeks of the study (p<0.001). Extended VBRT averaged higher monthly voucher costs compared to Standard VBRT ($96 vs $43, p<.001); however, the average cost per week of abstinence attained was higher in the Standard group ($8.06 vs $5.88, p<.001). Participants in the Extended group with voucher costs exceeding $25 monthly averaged 20 weeks of continuous abstinence.

Conclusions: Greater abstinence occurred during Extended VBRT, but providing a longer duration was not by itself sufficient to maintain abstinence after VBRT. However, if abstinence can be captured and sustained during VBRT, then providing longer durations may help increase the continuous abstinence that predicts better long-term outcomes.

Keywords: Cocaine abstinence; Reinforcement; Treatment duration; VBRT; Vouchers.

Conflict of interest statement

Conflict of Interest

All authors declare that they have no conflict of interest with regard to this research.

Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Figures

Figure 1

Participant Flow Diagram

Figure 2

Schematic of research procedures showing interventions and assessments implemented during each study week over all four study phases. Shaded bars indicate weeks when treatment (VBRT or Aftercare) and weekly urinalysis assessments were in effect. The final column indicates the type of analysis conducted with the data collected; LDA = Longest Duration of Abstinence, GEE = General Estimating Equation.

Figure 3

Condition and individual means for weeks of continuous cocaine-abstinence during study Phases 1 and 2 (months 1 through 6). Each data point represents an individual study participant’s maximum weeks of continuous abstinence. The bars represent the condition mean across participants for maximum weeks of continuous abstinence.

Figure 4

Mean percent of cocaine negative urine samples provided at each biweekly assessment during the 48-week study by condition and phase. Missing urine samples are treated as positive for cocaine. TAU signifies the Treatment as Usual phase (Methadone treatment only). Between group differences were significant in Phase 3.

Figure 5

Scatter plot showing incentive cost as a function of longest duration of abstinence attained during treatment. Each data point represents the results for one participant.