A systematic assessment of delay discounting in relation to cocaine and nicotine dependence.

Delay discounting is a measure of impulsivity describing how a reinforcer loses value as the delay to its receipt increases. Greater delay discounting is reliably observed among those with different substance use disorders (SUDs) compared to the general population. Nevertheless, the relation between delay discounting and the type and number of substances used remains unclear. The aim of this study was to compare delay discounting across four groups of participants: cocaine- and nicotine-dependent participants, cocaine-dependent only participants, nicotine-dependent only participants, and non-dependent controls. One hundred and seven participants completed a computerized delay discounting task for hypothetical monetary values. Data were fit to Mazur's hyperbolic equation to derive the discounting rate k. Results showed that delay discounting was significantly greater in the cocaine- and nicotine-dependent group, compared to the nicotine-dependent only group, compared to control group. Delay discounting was also greater in the cocaine-dependent only group relative to the nicotine-dependent only and control groups, but no differences were observed between the cocaine- and nicotine-dependent group and the cocaine-dependent only group. This study provides evidence that delay discounting differs depending on the type of SUD but not on the number of SUDs.