As the use of medicinal cannabis continues to rise, concerns about its impact on driving safety remain a hot topic. A new study published in the Journal of Safety Research (Schiemer et al., 2024) sheds light on how vaporized medicinal cannabis affects drivers’ hazard perception and risk-taking behaviors.
The Study: What They Tested
Researchers conducted a within-subjects experiment involving 38 medicinal cannabis patients who use prescribed flower. Participants completed video-based driving tests both before and after vaporizing their usual cannabis dose. These tests measured key driving skills such as:
- Hazard perception – The ability to detect and anticipate dangerous situations.
- Following distance – How closely drivers follow other vehicles.
- Gap acceptance – The willingness to merge into traffic gaps.
- Speed choice – The likelihood of exceeding safe speed limits.
The Findings: Perception vs. Reality
The results were intriguing. Objectively, there was no significant difference in hazard perception, following distance, speed choice, or gap acceptance after cannabis use. In other words, drivers did not perform worse on video-based driving tests after consuming cannabis.
However, subjectively, participants felt their hazard perception and ability to predict traffic conflicts were worse after consuming cannabis. This highlights a critical distinction: while actual driving-related skills may not decline, self-perception of impairment increases.
Why Does This Matter?
This research suggests that long-term medicinal cannabis patients who use their prescribed cannabis regularly may develop tolerance to its cognitive effects, preventing the driving impairments typically seen in occasional users. This aligns with previous studies showing that frequent cannabis users experience fewer cognitive disruptions than infrequent users.
Despite this, many cannabis users perceive themselves as impaired, which could lead to more cautious driving behaviors—possibly explaining why some previous studies have noted that cannabis users drive more conservatively after consumption.
The Legal Landscape: Still a Risk?
Even if actual impairment isn’t present, medicinal cannabis users still face legal risks. In many places, including Australia (where this study was conducted), zero-tolerance drug-driving laws apply. This means that having THC in your system—regardless of whether it impairs your driving—could still result in legal consequences.
In the U.S., cannabis-related DUI laws vary by state, with some requiring proof of actual impairment and others imposing strict per se limits on THC blood concentration. This study raises an important question: Should laws differentiate between recreational and medicinal users, especially those with established tolerance?
Final Thoughts
The latest research suggests that medicinal cannabis doesn’t necessarily impair driving performance, but it does influence how drivers perceive their own abilities. While more research is needed—particularly in real-world driving conditions—these findings challenge common assumptions about cannabis and road safety.
For cannabis patients, this study is both good news and a reminder to stay aware of how you feel after consuming your medicine. And for policymakers? It might be time to take another look at outdated, one-size-fits-all cannabis driving laws.
What’s your take? Should medicinal cannabis users be treated differently in DUI laws? Let us know in the comments!
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