More than 40% of drivers who died in motor vehicle crashes had high levels of active THC—the main compound in cannabis—in their systems, according to a new study.
These levels were far above the amount typically linked to impaired driving.
The findings raise important public health concerns and suggest that legalizing recreational marijuana has not changed the behavior of drivers who use the drug.
The study was presented at the 2025 American College of Surgeons Clinical Congress in Chicago. Researchers looked at data from 246 drivers who died in car crashes in Montgomery County, Ohio, between January 2019 and September 2024.
These drivers were tested for THC during autopsies, which routinely include drug screening. This time period also included the year Ohio legalized recreational cannabis, in 2023.
According to lead author Dr. Akpofure Ekeh, a surgery professor at Wright State University, the results were unexpected. The average THC level found in the drivers was 30.7 nanograms per milliliter (ng/mL). That’s much higher than the 2–5 ng/mL limit some states have set for legal driving.
These results show that most of the drivers used cannabis shortly before getting behind the wheel. “This isn’t about leftover THC in their system from days ago,” Dr. Ekeh said. “It shows recent use, probably right before driving.”
The study found that 103 drivers (41.9%) tested positive for THC. This percentage stayed relatively constant over the years, ranging from about 26% to 49% annually. Importantly, the rate of drivers testing positive didn’t change significantly after marijuana was legalized.
Before legalization, 42.1% tested positive, and after legalization, it was 45.2%. This suggests that making marijuana legal didn’t lead to more people driving under the influence—it was already a common issue.
Dr. Ekeh emphasized that while public discussion often focuses on the benefits of legal cannabis, there hasn’t been enough attention on the potential dangers. “People need to think of marijuana like alcohol,” he said. “If you wouldn’t drink and drive, you shouldn’t smoke and drive either.”
In summary, the study shows that cannabis use among drivers involved in deadly crashes is alarmingly high and has not been affected by legalization. With average THC levels far above safe limits, the data strongly suggest recent use that could impair driving.
These findings highlight the need for more public education and stricter safety messaging around cannabis use and driving.
For more health information, please read studies that one sleepless night can reverse depression for days and scientists find better treatment for older adults with depression.
Copyright © 2025 Knowridge Science Report. All rights reserved.
