Voucher-based reinforcement of cocaine abstinence in treatment-resistant methadone patients: effects of reinforcement magnitude.

Voucher-based reinforcement of cocaine abstinence has been one of the most effective means of treating cocaine abuse in methadone patients, but it has not been effective in all patients. This study was designed to determine if we could promote cocaine abstinence in a population of treatment-resistant cocaine abusing methadone patients by increasing the magnitude of voucher-based abstinence reinforcement. Participants were 29 methadone patients who previously failed to achieve sustained cocaine abstinence when exposed to an intervention in which they could earn up to $1155 in vouchers (exchangeable for goods/services) for providing cocaine-free urines. Each patient was exposed in counterbalanced order to three 9-week voucher conditions that varied in magnitude of voucher reinforcement. Patients were exposed to a zero, low and high magnitude condition in which they could earn up to $0, $382, or $3480 in vouchers for providing cocaine-free urines. Analyses for 22 patients exposed to all three conditions showed that increasing voucher magnitude significantly increased patients' longest duration of sustained cocaine abstinence (P<0.001) and percent of cocaine-free urines (P<0.001), and significantly decreased patients' reports of cocaine injections (P=0.024). Almost half (45%) of the patients in the high magnitude condition achieved >/=4 weeks of sustained cocaine abstinence, whereas only one patient in the low and none in the zero magnitude condition achieved more than 2 weeks. Reinforcement magnitude was a critical determinant of the effectiveness of this abstinence reinforcement intervention.