Polysubstance use is associated with deficits in substance-free reinforcement in college students

Diminished availability of substance-free reinforcement is a behavioral economic risk factor for dependence. The goal of this study was to determine the incremental effects of increasing levels of substance use (heavy drinking [HD], heavy drinking and marijuana use [HD + MJ], and polysubstance use) on levels of reinforcement related to substance-free activities and related constructs among college students.

Participants were 205 college students (53% female; 65% White, 26% African American; Mage = 19.5 years) who reported at least one heavy drinking episode (five/four or more drinks on one occasion for a man/woman) in the past month. Participants reported on past-month illicit drug use and substance-free activity reinforcement, time allocation, and depression.

A series of analyses of covariance indicated that heavy drinking, marijuana use, and other illicit drug (polysubstance) use was associated with lower total and peer-related substance-free reinforcement; less time spent exercising, studying or completing homework, and participating in extracurricular activities; and greater depression compared with HD alone. Polysubstance use was also associated with lower peer-related substance-free reinforcement compared with HD + MJ. Furthermore, those who engaged in HD + MJ use allocated less time to exercise and studying/homework compared with HD-alone participants.

Illicit drug use is associated with incremental deficits in substance-free reinforcement above and beyond heavy drinking. In particular, students who use illicit drugs other than marijuana may be at high risk and require intervention approaches that explicitly increase engagement in developmentally important substance-free activities such as academics.