Heroin and cocaine abusers have higher discount rates for delayed rewards than alcoholics or non-drug-using controls


Kris Kirby Bronfman Science Center Williams College Williamstown MA 01267 USA
Tel: 413 597 3143
Fax: 413 597 2085
E-mail: kkirby@williams.edu


Aims  To test a prediction of the discounting model of impulsiveness that discount rates would be positively associated with addiction. The delay-discount rate refers to the rate of reduction in the present value of a future reward as the delay to that reward increases.

Design and measurements  We estimated participants’ discount rates on the basis of their pattern of choices between smaller immediate rewards ($11–80) and larger, delayed rewards ($25–85; at delays from 1 week to 6 months) in a questionnaire format. Participants had a one-in-six chance of winning a reward that they chose on one randomly selected trial.

Participants and setting  Heroin (n = 27), cocaine (n = 41) and alcohol (n = 33) abusers and non-drug-using controls (n = 44) were recruited from advertisements. They were tested in a drug abuse research clinic at a medical school.

Findings  On average, the cocaine and heroin groups had higher rates than controls (both P < 0.001), but alcoholics did not (P = 0.44). Abstinence was associated with lower rates for heroin abusers (P = 0.03), but not for cocaine or alcohol abusers (both P > 0.50).

Conclusions  These data suggest that discount rates vary with the preferred drug of abuse, and that high discount rates should be considered in the development of substance abuse prevention and treatment efforts.