Impulsivity and Polysubstance Use: A Systematic Comparison of Delay Discounting in Mono-, Dual-, and Trisubstance Use

Understanding the association between polysubstance use and impulsivity is pertinent to treatment planning and efficacy. Delay discounting, a measure of impulsivity, supplies the rate at which a reinforcer loses value as the temporal delay to its receipt increases. Excessive delay discounting has been widely observed among drug-using individuals, though the impact of using more than 1 substance has been only minimally studied. Here, after controlling for demographic variables, we systematically compared delay discounting in community controls, heavy smokers, and alcohol-and cocaine-dependent individuals to assess the impact of non-, mono-, dual-, and trisubstance use. All substance-using groups discounted significantly more than did community controls (p < .05). Additionally, groups that smoked cigarettes in addition to another substance dependency discounted significantly more than did the group that smoked cigarettes only (p < .05). Last, trisubstance users who were alcohol-dependent, cocaine-dependent, and heavy cigarette smokers discounted significantly more than did heavy smokers (p < .01). However, trisubstance users did not discount significantly more than did any dual-substance group. Trisubstance use was associated with greater impulsivity than was monosubstance smoking but exhibited no greater impulsivity than did dual-substance use, suggesting a ceiling effect on discounting when more than 2 substances are in use. The present study suggests that smokers who engage in additional substance use may experience worse treatment outcomes, given that excessive discounting is predictive of poor therapeutic outcomes in several studies.