Discounting of delayed rewards in substance abusers: relationship to antisocial personality disorder.

RATIONALE: Delay discounting is associated with impulsivity and drug abuse, and this study evaluated the relationship between discounting of delayed rewards and antisocial personality disorder (ASP).

OBJECTIVES: To determine whether discounting is increased in substance abusers with ASP relative to those without; both groups were compared with non-substance-abusing controls.

METHODS: Subjects ( n=166) chose between hypothetical monetary amounts available after various delays or immediately. Under one condition, a US $1000 reward was delayed at intervals ranging from 6 h to 25 years. At each delay interval, the immediately available rewards varied from US $1 to US $999 until choices reflected indifference between the smaller immediate and larger delayed rewards. Under a second condition, the delayed reward was US $100, and immediate rewards varied from US $0.10 to US $99.90.

RESULTS: In all three groups, hyperbolic discounting functions provided a good fit of the data, and the smaller reward was discounted at a higher rate than the larger reward. Substance abusers discounted delayed rewards at significantly greater rates than controls, and substance abusers with ASP discounted delayed rewards at higher rates than their non-ASP substance-abusing counterparts. Discounting rates were correlated with impulsivity scores on a personality questionnaire.

CONCLUSIONS: These results provide further evidence of more rapid discounting of delayed rewards in substance abusers, especially among substance abusers with a co-morbid diagnosis of ASP.