Nearly half of drivers killed in crashes had THC in their blood

• Among 246 drivers who died in crashes, 41.9% had active THC in their blood, with an average level of 30.7 ng/mL -- far above the limits most states consider impairing.
• The high rate of THC detection remained steady over six years and did not change after the legalization of recreational cannabis.
• Researchers stress that public messaging about the risks of cannabis use while driving must be stronger and clearer.

High THC Levels Found in Fatal Crashes

A new analysis reveals that more than 40% of drivers who died in motor vehicle crashes tested positive for active delta-9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis. Average THC levels were many times higher than the concentrations known to cause impairment. According to the researchers, the findings point to a serious and ongoing public health concern that remains unaffected by the legalization of recreational marijuana.

The study was presented at the American College of Surgeons (ACS) Clinical Congress 2025, held in Chicago from October 4 to 7.

Examining Six Years of Data

Researchers reviewed coroner records from Montgomery County, Ohio, covering January 2019 through September 2024. The review included 246 deceased drivers who were tested for THC following fatal crashes. Toxicology screening is a standard part of the autopsy process, allowing for accurate postmortem detection of substances. The timeframe also included the state's 2023 legalization of recreational cannabis, giving the researchers a chance to assess whether policy changes influenced driver behavior.

"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."

Key Study Findings

• High Prevalence: 103 drivers (41.9%) overall tested positive for THC, with yearly rates ranging from 25.7% to 48.9%.
• No Effect from Legalization: The rate of drivers who tested positive for THC did not change significantly before or after legalization (42.1% vs. 45.2%), indicating that legal status did not influence the behavior of those who chose to drive after use.
• Consistent Over Time: The high rate of THC positivity showed no significant change over the six-year study period.

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 the average level in this study (30.7 ng/mL) far exceeded.

Stronger Warnings Urged

"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.

Citation: Ekeh A, et al. Cannabis Prevalence in Drivers Involved in Motor Vehicle Crash Fatalities over a 6-Year Period, Scientific Forum, American College of Surgeons (ACS) Clinical Congress 2025.

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.