Document Type
Article
Publication Date
12-2-2025
Abstract
BACKGROUND: Several US states have per se laws using 2 or 5 ng/mL of delta-9-tetrahydrocannabinol (THC) as cutpoints for driving under the influence of cannabis, while some have zero-tolerance statutes. These cutpoints are considered prima facia evidence of driving impairment.
METHODS: In a cohort of people who regularly use cannabis (N = 190) we measured baseline concentrations of THC after instructing participants to abstain from cannabis for at least 48 hours. Baseline driving performance was evaluated using a driving simulator. We also measured blood THC concentrations serially following a smoking session (placebo or active cannabis).
RESULTS: Forty-three percent of the participants exceeded zero-tolerance statutes (≥0.5 ng/mL) at baseline. Twenty-four percent had baseline blood THC concentrations that were ≥2 ng/mL and 5.3% were ≥5 ng/mL. The maximum observed baseline blood concentration was 16.2 ng/mL. Six hours after smoking active cannabis, the median (interquartile range) difference in THC concentrations compared with baseline was 0.5 (0-0.9) ng/mL; a 1-sample t-test comparing the mean change to 0 was significant (P < 0.001). There was no difference when comparing the mean change to 0 in the placebo group (P = 0.69). Simulated driving performance was not different between those who exceed zero tolerance and per se cutpoints vs those who are below these cutpoints (P > 0.05).
CONCLUSIONS: Many regular users of cannabis exceed zero tolerance and per se THC cutpoint concentrations days after their last use, risking legal consequences despite no evidence of impairment.
Recommended Citation
Fitzgerald, Robert L.; Umlauf, Anya; Suhandynata, Raymond T.; Grelotti, David J.; Huestis, Marilyn A.; Mastropietro, Kyle F.; Grant, Igor; and Marcotte, Thomas D., "Per Se Driving Under the Influence of Cannabis Statutes and Blood Delta-9-Tetrahydrocannabinol Concentrations following Short-Term Cannabis Abstinence" (2025). Institute of Emerging Health Professions Faculty Papers. Paper 33.
https://jdc.jefferson.edu/iehpfp/33
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Language
English
Comments
This article is the author’s final published version in Clinical Chemistry, Volume 71, Issue 12, 2025, Pages 1225-1233.
The published version is available at https://doi.org/10.1093/clinchem/hvaf121. Copyright © Association for Diagnostics & Laboratory Medicine 2025.