Medicinal cannabis users showed no decline in hazard perception after oral THC, but drove more cautiously and could not accurately self-assess their performance.
Medicinal cannabis patients who drive, prescribing physicians, traffic safety policymakers
No hazard perception decline, but self-assessment of impairment was unreliable
What the researchers found
Among 41 medicinal cannabis users, oral THC did not significantly impair hazard perception skill, but participants chose slower speeds and longer following distances after consumption. Critically, they could not accurately self-assess their performance regardless of whether they had consumed THC.
Why it matters
Medicinal cannabis patients need practical guidance about driving. This study suggests frequent users may compensate through cautious driving, but their inability to self-assess impairment remains a safety concern.
The numbers in context
N=41 medicinal cannabis users. No significant decline in hazard perception post-THC. Significantly slower speeds and longer following distances chosen. No correlation between perceived and actual performance.
How the study worked
Within-subjects study comparing 41 medicinal cannabis users on validated video-based driving measures at baseline (no THC) and after consuming oral THC oil.
What this study cannot tell us
Video-based measures, not actual driving. Moderate sample size. Participants knew they were being tested, which may have prompted extra caution. Tolerance effects from regular use likely played a role.
How to read the evidence
Within-subjects design with validated measures provides good internal validity, but moderate sample and video-based (not real driving) assessment limit conclusions.
When this study was published
2025 study of current medicinal cannabis users in clinical settings.
The bigger picture
Drug driving policy often treats all cannabis use equally, but this study suggests medicinal users who consume oral THC may behave differently than recreational users. The compensatory driving strategies are notable, as is the universal self-assessment failure.
Questions still open
- Do these compensatory strategies hold up in real-world driving? Should drug driving laws differentiate between medicinal and recreational cannabis users? Can any tool help patients assess their own driving fitness?
Common questions
Can medicinal cannabis patients drive safely after taking THC?
Do regular cannabis users develop tolerance to driving impairment?
Read the original research
The effects of orally ingested Delta-9-Tetrahydrocannabinol on drivers' hazard perception and risk-taking behaviours: A within-subjects study of medicinal cannabis users.
Psychopharmacology
Citation
Mieran, Taren; Hill, Andrew; Horswill, Mark S; Summers, Mathew J; Stefanidis, Kayla B. (2025). The effects of orally ingested Delta-9-Tetrahydrocannabinol on drivers' hazard perception and risk-taking behaviours: A within-subjects study of medicinal cannabis users.. Psychopharmacology. https://doi.org/10.1007/s00213-025-06869-w