Background: Chronic cocaine abuse remains a serious and costly public health problem. This study assessed the effectiveness of a voucher-based reinforcement contingency in producing sustained cocaine abstinence.
Methods: A randomized controlled trial compared voucher-based reinforcement of cocaine abstinence to noncontingent voucher presentation. Patients were selected from 52 consecutively admitted injecting heroin abusers in a methadone maintenance treatment program. Patients with heavy cocaine use during baseline period (N = 37) participated. Except where otherwise indicated, the term cocaine abuse is used in this article in a generic sense and not according to the DSM-III-R definition. Patients exposed to abstinence reinforcement received a voucher for each cocaine-free urine sample (ie, negative for benzoylecgonine) provided three times per week throughout a 12-week period; the vouchers had monetary values that increased as the number of consecutive cocaine-free urine samples increased. Control patients received noncontingent vouchers that were matched in pattern and amount to the vouchers received by patients in the abstinence reinforcement group.
Results: Patients receiving vouchers for cocaine-free urine samples achieved significantly more weeks of cocaine abstinence (P = .007) and significantly longer durations of sustained cocaine abstinence (P = .001) than controls. Nine patients (47%) receiving vouchers for cocaine-free urine samples achieved between 7 and 12 weeks of sustained cocaine abstinence; only one control patient (6%) achieved more than 2 weeks of sustained abstinence. Among patients receiving vouchers for cocaine-free urine samples, those who achieved sustained abstinence ( > or = 5 weeks) had significantly lower concentrations of benzoylecgonine in baseline urine samples than those who did not achieve sustained abstinence (P < or = .01). Patients receiving voucher reinforcement rated the overall treatment quality significantly higher than controls (P = .002).
Conclusion: Voucher-based reinforcement contingencies can produce sustained cocaine abstinence in injecting polydrug abusers.