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Δ 9 -Tetrahydrocannabinol (THC) impairs visual working memory performance: A randomized crossover trial

Kirsten C. S. Adam, Manoj K. Doss, Elisa Pabon, Edward K. Vogel, Harriet de Wit

bioRxiv (Cold Spring Harbor Laboratory) September 23, 2019 preprint DOI: 10.1101/778068 (opens in new tab)

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Study at a glance

AI-extracted from the abstract
Characteristics Randomized crossover experiment Double-blind
Sample size 46
Population Healthy adults
Dose 7.5 and/or 15 mg oral
Measures Discrete Whole-Report task, self-reported mind wandering, metacognitive accuracy
Topics Cannabis
Citations 2
Key findings THC impaired visual working memory performance (d = .65), increased mind wandering, and decreased metacognitive accuracy about task performance, indicating that THC's effect on working memory may relate to increased mind wandering and reduced monitoring.

Abstract

Abstract With the increasing prevalence of legal cannabis use and availability, there is an urgent need to identify cognitive impairments related to its use. It is widely believed that cannabis, or its main psychoactive component Δ 9 -tetrahydrocannabinol (THC), impairs working memory, i.e., the ability to temporarily hold information in mind. However, our review of the literature yielded surprisingly little empirical support for an effect of THC or cannabis on working memory. We thus conducted a study with 3 main goals: (1) quantify the effect of THC on visual working memory in a well-powered sample (2) test the potential role of cognitive effects (mind wandering and metacognition) in disrupting working memory, and (3) demonstrate how insufficient sample size and task duration reduce the likelihood of detecting a drug effect. We conducted two double-blind, randomized crossover experiments in which healthy adults ( N=23, 23 ) performed a reliable and validated visual working memory task (the “Discrete Whole-Report task”, 90 trials) after administration of THC (7.5 and/or 15 mg oral) or placebo. We also assessed self-reported ‘mind wandering’ (Exp 1) and metacognitive accuracy about ongoing task performance (Exp 2). THC impaired working memory performance ( d = .65), increased mind wandering (Exp 1), and decreased metacognitive accuracy about task performance (Exp 2). Thus, our findings indicate that THC does impair visual working memory, and that this impairment may be related to both increased mind-wandering and decreased monitoring of task performance. Finally, we used a down-sampling procedure to illustrate the effects of task length and sample size on power to detect the acute effect of THC on working memory.

Comparable studies

Other randomized controlled trials on cannabis, most cited first.

Study Year Design Participants
Cannabidiol inhibits THC-elicited paranoid symptoms and hippocampal-dependent memory impairment Healthy participants 2012 Randomized controlled trial n = 48
Distinct Effects of Δ9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing Healthy, English-native, right-handed men who had used cannabis 15 times or less in... 2009 Double-blind, randomized, placebo-controlled crossover trial n = 15
Acute Effects of a Single, Oral dose of d9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) Administration in Healthy Volunteers Healthy male subjects 2012 Randomized controlled trial n = 16
Modulation of Mediotemporal and Ventrostriatal Function in Humans by Δ9-Tetrahydrocannabinol Healthy, native English-speaking, right-handed men of white race/ethnicity who had used... 2009 Randomized controlled trial n = 15
Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition Healthy volunteers with a history of light cannabis use 2019 Randomized, double-blind, within-subjects crossover n = 14

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