Neurocognition in college-aged daily marijuana users

Abstract

Background: Marijuana is the most commonly used illicit substance in the United States. Use, particularly when it occurs early, has been associated with cognitive impairments in executive functioning, learning, and memory. Method: This study comprehensively measured cognitive ability as well as comorbid psychopathology and substance use history to determine the neurocognitive profile associated with young adult marijuana use. College-aged marijuana users who initiated use prior to age 17 (n = 35) were compared to demographically matched controls (n = 35). Results: Marijuana users were high functioning, demonstrating comparable IQs to controls and relatively better processing speed. Marijuana users demonstrated relative cognitive impairments in verbal memory, spatial working memory, spatial planning, and motivated decision making. Comorbid use of alcohol, which was heavier in marijuana users, was unexpectedly found to be associated with better performance in some of these areas. Conclusions: This study provides additional evidence of neurocognitive impairment in the context of adolescent and young adult marijuana use. Findings are discussed in relation to marijuana’s effects on intrinsic motivation and discrete aspects of cognition.

Keywords:

• Marijuana
• Neurocognition
• Decision making
• Memory
• Planning

Acknowledgements

We thank Snežana Urošević for helpful comments on prior versions of the manuscript. We also thank Brittany Schmaling for her contribution to data collection.

Funding

This study was supported by the National Institute on Drug Abuse [grant number R01DA017843] awarded to M. Luciana; the National Institute on Alcohol Abuse and Alcoholism [grant number R01AA020033] awarded to M. Luciana; and the University of Minnesota’s Center for Neurobehavioral Development. M. P. Becker was supported by the Pearson Assessment Fellowship in Clinical Psychology awarded by the Pearson Clinical Assessment Division. Disclosure: Role of funding source: Nothing declared. Funding sources had no involvement in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Conflict of interest:

No conflict declared by any authors.

Notes

¹ Note that the inclusion criterion of limiting alcohol use frequency to 4–5 drinks per occasion less than twice weekly still allows for the possibility of alcohol abuse symptoms.