Heroin delay discounting: Modulation by pharmacological state, drug-use impulsivity, and intelligence.

Abstract

Delay discounting (DD) refers to how rapidly an individual devalues goods based on delays to receipt. DD usually is considered a trait variable but can be state-dependent; yet few studies have assessed commodity valuation at short, naturalistically relevant time intervals that might enable state-dependent analysis. This study aimed to determine whether drug-use impulsivity and intelligence influence heroin DD at short (ecologically relevant) delays during two pharmacological states (heroin satiation and withdrawal). Out-of-treatment, intensive heroin users (n=170; 53.5% African-American; 66.7% male) provided complete DD data during imagined heroin satiation and withdrawal. Delays were 3, 6, 12, 24, 48, 72, and 96 hours; maximum delayed heroin amount was thirty $10 bags. Indifference points were used to calculate area under the curve (AUC). We also assessed drug-use impulsivity (subscales from the Impulsive Relapse Questionnaire, IRQ) and estimated intelligence (Shipley IQ) as predictors of DD. Heroin discounting was greater (smaller AUC) during withdrawal than satiation. In regression analyses, lower intelligence and IRQ Capacity for Delay as well as higher IRQ Speed (to return to drug use) predicted greater heroin discounting in the satiation condition. Lower intelligence and higher IRQ Speed predicted greater discounting in the withdrawal condition. Sex, race, substance use variables, and other IRQ subscales were not significantly related to the withdrawal or satiation DD behavior. In summary, heroin discounting was temporally rapid, pharmacological state-dependent, and predicted by drug-use impulsivity and estimated intelligence. These findings highlight a novel and sensitive measure of acute DD that is easy to administer.

Heroin delay discounting and impulsivity: Modulation by DRD1 genetic variation

“…Substance use characteristics were measured using the Drug History and Use Questionnaire (available on request). As previously described, delay discounting measures were obtained during two within‐subject, experimental conditions: imagined heroin satiation and withdrawal. The order of these two imagined conditions was randomized for each participant.…”

“…Initial analyses used repeated measures mixed‐model analysis of covariance (ANCOVA) with genotype as the between‐subjects factor (separate analysis for each genotype), pharmacological‐state condition (eg, heroin satiation vs withdrawal) as within‐subject factor and race and IQ as covariates. For any significant effects, we also conducted stepwise linear regression analyses, controlling for IQ, which explained variance in our earlier study and race because it is an important factor in genetic studies . We chose to conduct ANCOVA as the primary analysis with secondary linear regression because ANCOVA provides information about the initial significant interactions, whereas the subsequent regression allows us to more thoroughly consider the potential contributions of other covariates.…”

“…Traditional discounting methods assess DD over relatively long intervals (eg, months to years), which may not be ecologically relevant for a person using heroin every day . We previously examined heroin DD as a pharmacological‐state measure among regular heroin users, employing a condensed time scale to make the paradigm more relevant to real‐world drug use . The previous within‐subject study found that DD was dramatically steeper during an imagined opioid withdrawal than satiation condition.…”

“…The previous within‐subject study found that DD was dramatically steeper during an imagined opioid withdrawal than satiation condition. In the satiation condition, individuals with lower IQ and higher drug‐use impulsivity scores exhibited steeper heroin discounting …”

“…We hypothesized that dopamine genetic variation would be related to DD. On the basis of findings of our previous work on DD in heroin users, we also hypothesized that dopamine genetic variation would be associated with IQ and drug‐use impulsivity scores …”