Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition

Arkell, Thomas R.; Lintzeris, Nicholas; Kevin, Richard C.; Ramaekers, Johannes G.; Vandrey, Ryan G.; Irwin, Christopher; Haber, Paul; McGregor, Iain S. · 2019 · OpenAlex-citations

DOI: 10.1007/s00213-019-05246-8

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Summary

This study investigated whether cannabidiol (CBD) mitigates the impairing effects of delta-9-tetrahydrocannabinol (THC) on driving and cognitive performance. While CBD is often hypothesized to counteract THC-induced adverse effects, evidence remains inconsistent. The researchers aimed to compare the effects of vaporized THC-dominant cannabis against cannabis containing equivalent concentrations of THC and CBD, specifically assessing simulated driving and cognitive tasks. The study employed a randomized, double-blind, within-subjects crossover design involving 14 healthy adults with a history of infrequent cannabis use. Participants attended three experimental sessions separated by at least seven days, during which they vaporized 125 mg of either THC-dominant cannabis (11% THC, <1% CBD), THC/CBD-equivalent cannabis (11% THC, 11% CBD), or placebo (<1% THC/CBD). Performance was assessed using a high-fidelity driving simulator and three computerized cognitive tasks: the Digit Symbol Substitution Task (DSST), Divided Attention Task (DAT), and Paced Auditory Serial Addition Task (PASAT). Assessments occurred at two time points post-vaporization (20–60 minutes and 200–240 minutes). Plasma cannabinoid levels were also monitored via liquid chromatography-tandem mass spectrometry. Results indicated that both active cannabis conditions impaired driving and cognition relative to placebo. In the driving simulator, both THC-dominant and THC/CBD-equivalent cannabis significantly increased lane weaving (standard deviation of lateral position) during a car-following task. However, neither condition significantly affected other driving metrics such as speed or headway distance. Cognitive performance was impaired on all three tasks for both active conditions. Notably, impairment on the DAT and PASAT was worse following the THC/CBD-equivalent cannabis compared to the THC-dominant condition. Subjective drug effects, including feelings of being "stoned" and confidence in driving ability, did not differ between the two active cannabis types. Pharmacokinetic analysis revealed that peak plasma THC concentrations were higher after vaporizing the THC/CBD-equivalent cannabis, suggesting a pharmacokinetic interaction where CBD may potentiate THC absorption. The study concludes that cannabis containing equivalent amounts of CBD and THC is no less impairing than THC-dominant cannabis regarding driving and cognitive performance. In some cognitive domains, CBD may actually exacerbate THC-induced impairment. These findings challenge the assumption that CBD mitigates the psychoactive risks of THC in this context and suggest that the presence of CBD does not render cannabis safer for driving. The observed increase in plasma THC levels with the combined product highlights the need for further investigation into the pharmacokinetic interactions between these cannabinoids.

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• cannabis
• polydrug