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Combined effect of alcohol and cannabis on simulated driving.

Andrew Fares, Christine M Wickens, Robert E Mann, Patricia Di Ciano, Madison Wright, Justin Matheson, Omer S M Hasan, Jurgen Rehm, Tony P. George, Andriy V Samokhvalov, Paul A Shuper, Marilyn A. Huestis, Gina Stoduto, Timothy Brown, Cristiana Stefan, Dafna Sara Rubin-Kahana, Bernard Le Foll, Bruna Brands

Psychopharmacology May 2022 DOI: 10.1007/s00213-021-05773-3 (opens in new tab)

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Study at a glance

AI-extracted from the abstract
Characteristics Randomized clinical trial (within-subjects, double-blind, double-dummy, placebo-controlled) Peer reviewed
Population Cannabis users aged 19-29 years who used cannabis 1-7 days per week
Interventions Smoked cannabis Alcohol
Dose Cannabis 12.5% THC; alcohol target BrAC 0.08%
Measures Standard deviation of lateral position, reaction time, subjective drug effects, cardiovascular measures, self-reported perception of driving ability (driving ability questionnaire), whole blood THC and metabolite concentrations
Topics Cannabis
Keywords Alcohol Driving Reaction time Subjective effects Weaving
Key findings Combining smoked cannabis (12.5% THC) with alcohol (target BrAC 0.08%) increased weaving (standard deviation of lateral position) relative to placebo and, in some drive segments, relative to alcohol or cannabis alone, and increased reaction time relative to placebo. The authors suggest a potential additive effect, and participants appeared unaware of their level of impairment on a driving-ability questionnaire.

Abstract

With alcohol and cannabis remaining the most commonly detected drugs in seriously and fatally injured drivers, there is a need to understand their combined effects on driving. The present study examined the effects of combinations of smoked cannabis (12.5% THC) and alcohol (target BrAC 0.08%) on simulated driving performance, subjective drug effects, cardiovascular measures, and self-reported perception of driving ability. In this within-subjects, double-blind, double-dummy, placebo-controlled, randomized clinical trial, cannabis users (1-7 days/week) aged 19-29 years attended four drug administration sessions in which simulated driving, subjective effects, cardiovascular measures, and whole blood THC and metabolite concentrations were assessed following placebo alcohol and placebo cannabis (<0.1% THC), alcohol and placebo cannabis, placebo alcohol and active cannabis, and alcohol and active cannabis. Standard deviation of lateral position in the combined condition was significantly different from the placebo condition (p < 0.001). Standard deviation of lateral position was also significantly different from alcohol and cannabis alone conditions in the single task overall drive (p = 0.029 and p = 0.032, respectively), from the alcohol alone condition in the dual task overall drive (p = 0.022) and the cannabis alone condition in the dual task straightaway drive (p = 0.002). Compared to the placebo condition, the combined and alcohol conditions significantly increased reaction time. Subjective effects in the combined condition were significantly greater than with either of the drugs alone at some time points, particularly later in the session. A driving ability questionnaire showed that participants seemed unaware of their level of impairment. Combinations of alcohol and cannabis increased weaving and reaction time, and tended to produce greater subjective effects compared to placebo and the single drug conditions suggesting a potential additive effect. The fact that participants were unaware of this increased effect has important implications for driving safety.

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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