Chronic Marijuana Use, Inhibitory Control, and Processing Speed in Young Adult College Students

Abstract

Marijuana is the most widely used illicit substance in the United States, and its use is especially prevalent among young adults. Over the past two decades, there has been an overall decline in perceived harmfulness of marijuana use in young adults ages 18-30, despite growing evidence that chronic marijuana use may be associated with cognitive impairment. There have been mixed results regarding the effects of chronic marijuana use on inhibitory control. Furthermore, previous literature has shown inconsistent results regarding processing speed in marijuana users. The current study examined inhibitory control and processing speed in chronic marijuana-using young adult college students and healthy controls ages 18-22. 33 healthy controls (mean age: 19.18 ± 1.13; 18 male) and 28 chronic marijuana users (mean age: 20.25 ± 1.17; 19 male) were included in the study. Chronic marijuana users had to have used marijuana ≥5 times/week over the past year to be eligible. Participants were instructed to remain abstinent from marijuana use for 12 hours prior to the study visit. The 30-day Timeline Followback (TLFB) was used to assess recent marijuana use and participants were asked to estimate age at first marijuana use and lifetime days of marijuana use. Participants completed the Stroop Color Word Task (SCWT), and the interference t-score was used as a measure of inhibitory control. Furthermore, we examined marijuana use characteristics (i.e. age at first use, lifetime marijuana use, and past 30-day marijuana use) in relation to performance on the SCWT. Additionally, exploratory analyses investigated differences in the color and word conditions of the SCWT between the two groups and as a function of marijuana use characteristics. Results indicated no significant group differences on the interference, word, and color conditions of the SCWT. Furthermore, there were no significant correlations between age at first use, lifetime marijuana use, and past 30-day marijuana use with any conditions of the SCWT, but, there was a trend for greater past 30-day marijuana use to be associated with poorer performance on the color condition (r(26) = -0.26, p = 0.09). These findings indicate that chronic, heavy marijuana use may not be associated with impairments in inhibitory control or processing speed, which is consistent with other studies examining current use, heavy use, and chronic use in adolescents, young adults, and adults. Further research is needed to determine whether chronic, heavy marijuana use during young adulthood affects higher-order cognitive functioning skills needed for success in college, starting a career, and transitioning into adulthood.