Tashia Petker, MSc; Max M. Owens, PhD; Michael T. Amlung, PhD; Assaf Oshri, PhD; Lawrence H. Sweet, PhD; James MacKillop, PhD
Background: There is evidence that heavy cannabis use is associated with decrements in cognitive performance, but findings are mixed and studies are often limited by small sample sizes and narrow adjustment for potential confounding variables. In a comparatively large sample, the current study examined associations between multiple indicators of cannabis use in relation to performance on a variety of neuropsychological tasks.
Methods: Participants were 1121 adults (54% female) enrolled in the Human Connectome Project. Cannabis involvement comprised recent cannabis use (positive tetrahydrocannabinol screen), total number of lifetime uses, cannabis use disorder and age at first use. The neuropsychological battery comprised performance in episodic memory, fluid intelligence, attention, working memory, executive function, impulsive decision-making, processing speed and psychomotor dexterity. Covariates were age, sex, income, family structure and alcohol and tobacco use.
Results: Positive urinary tetrahydrocannabinol status was associated with worse performance in episodic memory and processing speed, and positive cannabis use disorder status was associated with lower fluid intelligence (all p < 0.005). No other significant associations were present.
Limitations: The sample was limited to young adults aged 22–36 years. The measures of cannabis involvement were relatively coarse.
Conclusion: Beyond an array of potential confounders, recent cannabis use was associated with deficits in memory and psychomotor performance, and cannabis use disorder was associated with lower overall cognitive functioning in a large normative sample of adults. The findings pertaining to recent use have particular relevance for occupational settings.
Submitted Jul. 23, 2018; Revised Dec. 20, 2018; Accepted Feb. 17, 2019; Published online June 27, 2019
Acknowledgements: The data used in this project are from the Human Connectome Project, WU-Minn Consortium (principal investigators: David Van Essen and Kamil Ugurbil; 1U54MH091657) funded by the 16 National Institutes of Health (NIH) institutes and centres that support the NIH Blueprint for Neuroscience Research; and by the McDonnell Center for Systems Neuroscience at Washington University in St. Louis. The authors are deeply appreciative of the Human Connectome Project for open access to its data. In addition, the work was partially supported by the Peter Boris Chair in Addictions Research (J. MacKillop) and the Gary Sperduto Endowed Professorship in Clinical Psychology (L. Sweet). No funding sources were involved in study design or collection, or in the analysis and interpretation of the data. These findings do not reflect the official position of the National Institutes of Health.
Affiliations: From the Peter Boris Centre for Addictions Research, McMaster University/St. Joseph’s Healthcare Hamilton, Hamilton, Ont., Canada (Petker, Amlung, MacKillop); the Department of Psychology, Neuroscience, and Behaviour, McMaster University, Hamilton, Ont., Canada (Petker, Amlung, MacKillop); the Addiction Medicine Service, Homewood Health Centre, Guelph, Ont., Canada (Petker, Owens); the Department of Psychology, University of Georgia, Athens, GA, USA (Sweet, MacKillop); the Michael G. DeGroote Centre for Medicinal Cannabis Research, McMaster University/St. Joseph’s Healthcare Hamilton, Hamilton, Ont., Canada (Amlung, MacKillop); the Department of Human Development and Family Science, University of Georgia, Athens, GA, USA (Oshri); the Department of Psychiatry and Human Behavior, Alpert Medical School of Brown University, Providence, RI, USA (Sweet); and the Homewood Research Institute, Guelph, Ont., Canada (MacKillop).
Competing interests: J. MacKillop is a principal in BEAM Diagnostics, Inc. No other competing interests declared.
Contributors: T. Petker and J. MacKillop designed the study. The data were provided by the Washington University–University of Minnesota Consortium Human Connectome Project. T. Petker analyzed the data and all authors interpreted the findings. T. Petker drafted the article, which was edited and augmented by the other authors. All authors approved the final version to be published and can certify that no other individuals not listed as authors have made substantial contributions to the paper.
Correspondence to: J. MacKillop, McMaster University, 100 West 5th St., Hamilton, ON L8N 3K7; email@example.com