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Association of Driving with Blood THC: A Systematic Review
28 Pages Posted: 18 Oct 2024
More...Abstract
Background: Driving under the influence of cannabis increases the risk of motor vehicle collisions. In some jurisdictions, deterrence rests on the ability to detect delta-9-tetrahydrocannabinol (THC) in blood. Recent evidence suggests that there may be a nuanced relationship of blood THC to driving. The purpose of this systematic review was to summarize all published papers investigating the presence of a relationship between blood THC and driving, primarily measured by simulated driving in the lab.
Methods: The systematic review was completed according to PRISMA, and the protocol was pre-registered (PROSPERO CRD42023493758). All peer-reviewed studies that measured the strength of the linear relationship between driving outcomes and blood THC, up to September 2023 were included. The studies were appraised using SIGN Methodology Checklists. The main outcomes assessed included ‘weaving’/lateral control (e.g., standard deviation of lateral position (SDLP)), speed, car following (following distance; coherence), reaction time, and overall driving performance.
Findings: Of the 4,845 records from the literature search, only 12 met the criteria. 10 of these reported no significant linear correlations between blood THC and measures of driving (8 out of 9 for ‘weaving’/lateral control, 4 out of 5 for speed, 2 of 3 for car following tasks (coherence / headway maintenance task), 1/1 for reaction time, 3/3 for overall driving performance). The studies that did find an association between driving and blood THC employed complex driving situations.
Interpretation: This synthesis has important implications for road safety given driving situations can be complex due to challenging road situations and increases in potency of cannabis over the past years. Current methods of detection of impairment may be suited to some types of situations but more large-scale studies on the relationship of blood THC and driving are needed that systematically vary driving complexity and cannabis potency.
Funding: This study did not receive specific funding.
Declaration of Interest: Dr. Bernard Le Foll has obtained funding from Indivior for a clinical trial sponsored by Indivior. Dr. Le Foll has in-kind donations of placebo edibles from Indivia. Dr. Le Foll has obtained industry funding from Canopy Growth Corporation (through research grants handled by the Centre for Addiction and Mental Health and the University of Toronto). He has participated in a session of a National Advisory Board Meeting (Emerging Trends BUP- XR) for Indivior Canada and is part of Steering Board for a clinical trial for Indivior. He has been consultant for Shinogi and ThirdBridge. He got travel support to attend an event by Bioprojet. He is supported by CAMH, Waypoint Centre for Mental Health Care, a clinician-scientist award from the department of Family and Community Medicine of the University of Toronto and a Chair in Addiction Psychiatry from the department of Psychiatry of University of Toronto. No other authors have any conflicts to declare.
Keywords: Cannabis, SDLP, speed, reaction time
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