THC-impaired driving deaths are soaring, according to new study findings that will be presented this week at the American College of Surgeons (ACS) Clinical Congress 2025 in Chicago.

In a review of 246 deceased drivers from Montgomery County in Ohio from January 2019 to September 2024, 41.9 percent tested positive for active delta-9-tetrahydrocannabinol (THC) in their blood, with an average level of 30.7 ng/mL — far exceeding most state impairment limits.

The high rate of THC positivity remained consistent over six years and was unaffected by the state’s legalization of recreational cannabis during the study period in 2023.

The rate of drivers who tested positive for THC did not change significantly before or after legalization (42.1 percent vs. 45.2 percent), indicating that legal status did not influence the behavior of those who chose to drive after use.

The results of the study prompted the authors to recommend stronger messaging around the dangers of smoking cannabis while driving.

“I was surprised to see that level,” said lead author Akpofure P. Ekeh, MBBS, FACS, a professor of surgery at Wright State University in Dayton, Ohio. “An average level of 30.7 ng/mL generally means those people must have consumed marijuana at some time close to driving. This isn’t about residual use; it’s about recent consumption.”

The study notes that blood THC levels are typically drawn by the coroner within hours of death, providing an accurate snapshot of a driver’s state at the time of the crash.

Most states that have set legal limits for driving range from 2 to 5 nanograms per milliliter (ng/mL) — a threshold that the average level in this study (30.7 ng/mL) far exceeded.

“The messaging over the last few years has been just the push towards recreational legalization,” Dr. Ekeh noted. “The problem is that from a public health standpoint, there has not been enough emphasis on some of the downsides and the dangers that can occur. People should treat smoking marijuana just like they treat alcohol: don’t smoke and drive.”

Co-authors are Lois Nguapa, BS; Clara Mussin Phillips, BS; and Ann Cardosi, BS, MPH.

Note: This research was presented as an abstract at the ACS Clinical Congress Scientific Forum. Research abstracts presented at the ACS Clinical Congress Scientific Forum are reviewed and selected by a program committee but are not yet peer reviewed.