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

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.