We talk about acute effects of cannabis use (THC) on driving performance with Tom Marcotte, a clinical scientist with decades of experience in this area. We cover the acute cognitive effects of cannabis, the time course of the effects of cannabis on driving performance (based on a driving simulator), the relationship between subjective perceptions of driving performance and actual performance, relevant legal and legislative issues related to cannabis and driving, and differences between recreational and medicinal cannabis on cognition and driving.
A pdf of the transcript for this episode is available here.
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Topics Covered
- Terminology (e.g., difference between “marijuana” and “cannabis”)
- Acute cognitive effects of cannabis on driving
- Whether or not legalizing cannabis has affected accident rates
- Methodology, results, and implications of Tom’s recent study on cannabis and driving published in JAMA Psychiatry, including:
- Quantity/dosage effects
- Topography of smoking cannabis
- Whether or not blood alcohol level is useful for determining driving safety
- What aspects of driving were affected
- Time course of the effects
- Resiliency to negative effects
- Participants’ perceptions of their driving ability/safety
- Difference between smoking and ingesting cannabis
About Tom
Dr. Thomas Marcotte is Professor of Psychiatry at the University of California, San Diego, and Co-Director of the Center for Medicinal Cannabis Research, which has conducted clinical trials of cannabis for over 20 years and has an active, ongoing portfolio exploring the effects of cannabinoids (plant-based, synthetic) in various medical/psychiatric conditions. He is currently the principal investigator on studies addressing the effects that cannabis has on driving performance, both alone and in combination with alcohol, including methods for detecting cannabis-related driving impairment (bodily fluids, standardized field sobriety tests, and tablet-based measures). He is also the principal investigator of an NIH-funded take-home study of cannabis for the treatment of pain, and previously was a co-investigator on cannabis studies addressing pain and spasticity in multiple sclerosis. Dr. Marcotte has served on the editorial boards of Neuropsychology and the Journal of the International Neuropsychological Society, was co-chair of the Research, Data and Technology subcommitte of the State of California Impaired Driving Task Force, and a member on the California Office on Traffic Safety Impaired Driving Blueprint Roundtable. He is co-editor of the book Neuropsychology of Everyday Functioning, 2nd Edition (Marcotte, Schmitter-Edgecombe & Grant).
Selected Resources
Link to Tom’s JAMA Psychiatry article
Map of marijuana legality by state
UCSD Center for Medicinal Cannabis Research (CMCR)
Selected References
Broyd, S. J., van Hell, H. H., Beale, C., Yuecel, M., & Solowij, N. (2016). Acute and chronic effects of cannabinoids on human cognition: A systematic review. Biological Psychiatry, 79(7), 557-567.
Dellazizzo, L., Potvin, S., Giguère, S., & Dumais, A. (2022). Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: a systematic meta-review of meta-analyses. Addiction.
Lenné, M. G., Dietze, P. M., Triggs, T. J., Walmsley, S., Murphy, B., & Redman, J. R. (2010). The effects of cannabis and alcohol on simulated arterial driving: Influences of driving experience and task demand. Accident Analysis & Prevention, 42(3), 859-866.
Marcotte, T. D., Umlauf, A., Grelotti, D. J., Sones, E. G., Sobolesky, P. M., Smith, B. E., Hoffman, M. A., Hubbard, J. A., Severson, J., Huestis, M. A., Grant, I., & Fitzgerald, R. L. (in press). Driving performance and cannabis users’ perception of safety: A randomized clinical trial of smoked cannabis of different THC content. JAMA Psychiatry.
Ramaekers, J. G. (2018). Driving under the influence of cannabis: an increasing public health concern. JAMA,319(14), 1433-1434.