Δ9-Tetrahydrocannabinol (THC) impairs visual working memory performance: a randomized crossover trial

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 three 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 = 0.65), 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.

Classic Visual Search Effects in an Additional Singleton Task: An Open Dataset

“…Indeed, in some cases, we even found distractor presence benefits whereby participants found the target faster when a salient singleton distractor was present. Because of the fairly large number of trials per participant that we collected (e.g., 1600 in Experiment 1) we anticipate this dataset will be useful for modeling the effects of stimulus history and non-target homogeneity (Calder-Travis & Ma, 2020;Mihali & Ma, 2020;Rosenholtz, 2001;Tseng et al, 2014) as well as for sub-sampling analyses to estimate the effect of trial counts on expected power for new within-and between-subjects task variants (Adam et al, 2020;Baker et al, 2020;Ngiam et al, 2021;Xu et al, 2017).…”

Consensus recommendations on dosing and administration of medical cannabis to treat chronic pain: results of a modified Delphi process

“…Clinicians may feel comfortable with tailoring the medical cannabis treatment regimen knowing that patients are not at a significant overdose death risk. However, cannabis-associated health risks including Cannabis Use Disorder and complications resulting from the psychoactive effects of THC need to be considered, even at low doses (Adam et al 2020). This concept is important for the operation of motor vehicles, as well as occupational and recreational hazardous activity.…”

Cannabis and Cognitive Functioning: From Acute to Residual Effects, From Randomized Controlled Trials to Prospective Designs

“…Reconciliation of these contradictory findings is challenging considering the heterogeneity in the tasks used. A detailed analysis of 15 published studies assessing the dose effects of 9 -THC on digitspan performance, demonstrated that negative results may be due to short task length (and low number of trials, e.g., 3min Digit Span task), which imparts lower sensitivity to detect an effect compared to longer task durations (39). Altogether, there is converging evidence that the cannabis impairing effects on verbal learning and memory, response inhibition, and psychomotor speed occur in a dose-response fashion.…”

“…Specifically for attention and working memory domains, the literature reports mixed findings: while most studies observed that the severity of impairments are a function of Δ 9 -THC content or performance is solely affected by the higher dose ( 30 – 32 , 34 , 35 , 38 , 39 ), some found that these domains were unaffected by Δ 9 -THC ( 32 , 34 , 36 ). Reconciliation of these contradictory findings is challenging considering the heterogeneity in the tasks used.…”