Objective: Substance dependent individuals (SDIs) typically overvalue immediate and undervalue (discount) delayed rewards, and level of discounting significantly predicts posttreatment relapse and other behavioral outcomes. Delay discounting has potential significance for studies of HIV prevention and adherence to antiretroviral therapy; but effects of HIV infection on delay discounting rates among SDIs are not well understood, although discounting rates are higher among individuals infected with hepatitis C virus (HCV). In this study, we investigated potential additive or interactive effects of HIV and HCV infection on delay discounting performance among a group of 239 SDIs with verified HIV and HCV serostatus. Method: All participants were verified abstinent from drugs and alcohol at testing. All participants completed measures of substance abuse characteristics and comorbid disorders, and the Monetary Choice Questionnaire, a well-known measure used to derive k coefficients, which index discounting rates. Results: Groups were comparable on demographic, substance use, and comorbid characteristics. Compared with uninfected controls, discounting rates were significantly higher among individuals seropositive for HCV but not HIV. Additionally, no significant group differences in discounting rates were observed among HCV+ participants with or without coinfection with HIV. Group differences could not be attributed to aging or nonspecific effects of drug addiction. Additionally, increased discounting rates were associated with riskier injection practices. Conclusions: Potential mechanisms contributing to this discrepancy in discounting rates between HIV+ and HCV+ SDIs, including decision making, are discussed and await further study.
