Impulsivity and polysubstance use: A systematic comparison of delay discounting in mono, dual, and tri-substance 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 one substance has been only minimally studied. Here, after controlling for demographic variables, we systematically compare delay discounting in community controls, heavy smokers, alcohol-dependent, and cocaine-dependent individuals to assess the impact of non-, mono-, dual-, and tri-substance use. All substance-using groups discount significantly more than community controls ( p < 0.05). Additionally, groups that smoke cigarettes in addition to another substance dependency discount significantly more than cigarette smoking alone ( p < 0.05). Lastly, tri-substance users who were alcohol-dependent, cocaine-dependent and heavy cigarette smokers discount significantly more than heavy smokers ( p < 0.01). However, tri-substance users do not discount significantly more than any dual-substance group. Tri-substance use is associated with greater impulsivity than mono-substance smoking, but no greater impulsivity than dual-substance users, suggesting a ceiling effect on discounting when more than two 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.