How THC and CBD Affect Driving Performance: Research Studies Discussed in Healer Webinar

Does cannabis impair driving performance? This month’s Healer webinar, hosted by hosted by Dustin Sulak, DO, included an analysis of three recently published studies on THC or CBD and the effects on simulated driving tests. Dr. Sulak noted that these studies did not focus on the effect of cannabis on driving performance in medical cannabis users.

Read additional studies on Tourette syndrome, chemotherapy-induced neuropathy, and caregiver wellbeing, also covered in this webinar.

Research on THC and Crash Risk

The first study discussed was “Understanding cannabis use and car crashes: Insights from a randomized trial using a driving simulator on THC blood levels and subjective measures of sleepiness and performance,” which was published in the Journal of Safety Research online in September 2025. This study involved 30 male participants ages 18–30 years old, who used cannabis either occasionally (considered 1-2 joints per week) or chronically (considered 1-2 joints per day). The study compared the effects of three doses of THC (placebo, 10 mg, and 30 mg) on driving performance and subjective feelings of awareness, confidence, confusion, etc.

Crashes were seen most often at four hours after inhaling 10 mg of THC and 30 mg of THC. This did not coincide with the maximum THC levels period, typically within five to fifteen minutes after inhalation. Additionally, no significant differences were seen between chronic and occasional users.

Dr. Sulak noted the interindividual variability in the results. “For some people, it doesn’t matter if they have 10 mg of THC or 30 mg, they’re still crashing, which means we can’t have a cookie cutter rule," he stated. "What we need are methods for determining if you’re impaired or not and responding appropriately.” He also noted that the participants’ confidence also seemed to be related to the risk of crashes. “You need personal responsibility over your cannabis use and your ability to drive,” he added, as a take home message from the results.

Driving After Abstaining from Cannabis

The next study, “Short-term residual effects of smoked cannabis on simulated driving performance,” was published in Psychopharmacology in September 2025. Examining driving performance after 48 hours of abstinence from cannabis, this two-part study included a driving simulator involving 191 participants along with a comparison of 18 participants who had the highest cannabis use and 12 participants did not use cannabis. Results from the 25-minute driving simulator found no relationship between driving performance and cannabis use history or demographics. The comparison also demonstrated no difference between driving performance between the participants who smoked and at least 1 g of cannabis on 28 out of the past 30 days and participants in a control group.

“So the finding of this study was basically nothing, there's no evidence of a dose effect relationship,” Dr. Sulak summarized, though he noted some limitations and broader applications of the data. “It didn't measure reaction time. It also didn't measure cannabis withdrawal symptoms, even though none were reported. This is part of the bigger picture of wondering whether cannabis use, whether it’s light, moderate, or heavy, does it have a long-term impact on cognition, on performance, on reaction time? And most of the adult data out there using cognitive tests suggest no, that after a certain period of absence, people return to their baseline function. The brain is not going to be impaired long term from using cannabis, even after a short break.”

CBD and Driving Safety: Visual Function

The last study discussed was “Visual function and vehicle driving performance under the effects of cannabidiol: A randomized cross-over experiment,” which was published in Addiction in January 2025. This double-blind, placebo-controlled study involved 30 participants who were occasional cannabis or CBD users. Three tests were conducted, each a week apart, with vaporized doses of CBD: a placebo, 15% CBD (16 mg) or 30% CBD (32 mg). Measurements were taken for driving performance and visual function, including static and dynamic visual acuity, contrast sensitivity, and motion detection. Overall, apart from a decrease in motion detection, the CBD doses did not seem to have an effect on driving performance or visual function.

In reference to the decrease in motion detection, Dr. Sulak examined the potential effects of CBD on relaxing the participant. “Is CBD relaxing people’s anxiety and making them less reactive, less hyper vigilant, less responsive?” he stated. “But then again, too much anxiety or hyper vigilance can actually make people worse drivers. There’s tradeoffs for sure.”