The effects of orally ingested Delta-9-Tetrahydrocannabinol on drivers' hazard perception and risk-taking behaviours: A within-subjects study of medicinal cannabis users.
Taren Mieran, Andrew Hill, Mark S Horswill, Mathew J Summers, Kayla B Stefanidis
Psychopharmacology March 1, 2026 DOI: 10.1007/s00213-025-06869-w (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Within-subjects design Peer reviewed |
|---|---|
| Sample size | 41 |
| Population | Medicinal cannabis users |
| Intervention | THC oil |
| Topics | Cannabis |
| Keywords | Delta-9-tetrahydrocannabinol Hazard perception skill Road safety |
| Key points | Orally ingested THC did not impair actual hazard perception skill in medicinal cannabis users, but they drove slower and followed at longer distances after consumption. |
Abstract
Medicinal cannabis use is increasing worldwide, yet its impacts on driving safety in frequent users are not clearly understood. A more comprehensive understanding of the effects of THC on driving behaviour in frequent users is needed to guide drug driving policy and evidence-based advice for medicinal cannabis consumers. This study investigated the acute effects of orally ingested THC oil on medicinal cannabis users': (a) hazard perception skill performance; (b) driving-related risk-taking behaviours (speeding propensity, following distance, gap acceptance); (c) self-perceived hazard perception skill performance; and (d) self-perceptions of driving skills and safety. A within-subjects design was used to compare scores on validated video-based measures of hazard perception skill and risk-taking behaviours, along with self-report measures, between baseline (no THC) and post-consumption. Although participants' (N = 41) actual hazard perception skill performance did not significantly decline from baseline to post-consumption, their perceived performance did (with no significant correlation between the two in either condition). In the other video-based measures, participants selected significantly slower speeds and longer following distances post-consumption (but gap acceptance behaviour was unchanged). There was no significant change in self-perceptions of driving skills and safety after correction for multiple tests. While there was no evidence that oral ingestion of THC oils by medicinal cannabis users impacted hazard perception skill performance, they were unable to accurately self-assess their performance, regardless of whether they had consumed THC. Further, medicinal cannabis patients engage in compensatory strategies, specifically by reducing their speed and increasing their following distance following the consumption of THC.
Comparable studies
Other experimental studies on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Smoked Cannabis' Psychomotor and Neurocognitive Effects in Occasional and Frequent Smokers Occasional (<2x/week) and frequent (≥4x/week) cannabis smokers | 2015 | Controlled within-subjects study | n = 25 |
| Dissociable effects of cannabis with and without cannabidiol on the human brain’s resting-state functional connectivity Healthy volunteers experienced with cannabis but not regular users | 2019 | Within-subjects experimental design | n = 17 |
| Which biological and self-report measures of cannabis use predict cannabis dependency and acute psychotic-like effects? Young cannabis users | 2018 | Observational study (naturalistic, within-subject counterbalanced design) | n = 410 |
| Cannabis Essential Oil: A Preliminary Study for the Evaluation of the Brain Effects Healthy volunteers | 2018 | Experimental study | n = 5 |
| Coming off cannabis: a cognitive and magnetic resonance imaging study in patients with multiple sclerosis Patients with multiple sclerosis who began using cannabis after disease onset, used it... | 2019 | Quasi-experimental study with odd-even allocation | n = 40 |
Citations in the library
Cites 8
- Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition Psychopharmacology May 1, 2019
- Tolerance and cross-tolerance to neurocognitive effects of THC and alcohol in heavy cannabis users Psychopharmacology October 30, 2010
- Smoked Cannabis' Psychomotor and Neurocognitive Effects in Occasional and Frequent Smokers Journal of Analytical Toxicology March 4, 2015
- Does cannabidiol make cannabis safer? A randomised, double-blind, cross-over trial of cannabis with four different CBD:THC ratios Neuropsychopharmacology November 16, 2022
- Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial. JAMA Psychiatry March 1, 2022
and 3 more in the library