Chicago — A recent study of 246 drivers killed in traffic crashes over a nearly six-year period found that over 40% had active THC – the main psychoactive ingredient in cannabis – in their system.
In addition, average THC blood levels far exceeded what’s considered to cause impairment.
A team led by a Wright State University researcher analyzed coroner records in Ohio’s Montgomery County from January 2019 to September 2024. (The state legalized recreational marijuana use in 2023.) The coroner typically draws blood within hours of death to analyze levels of THC.
The researchers found that 103 of the drivers (41.9%) tested positive for THC, with annual positivity ranging from 25.7% to 48.9% over the study period.
The percentage of THC positivity showed no significant change before (42.1%) and after (45.2%) legalization, “indicating that legal status did not influence the behavior of those who chose to drive after use.”
Lead study author Akpofure P. Ekeh, a professor of surgery at Wright State in Dayton, said the average THC level among drivers who tested positive was 30.7 nanograms per millimeter. Most states, according to an American College of Surgeons press release, have set legal THC limits for driving from 2 to 5 ng/mL.
“I was surprised to see that level,” Ekeh said. “An average 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.”
From a public health standpoint, Ekeh said that more messaging is needed on the dangers of THC and driving. “People should treat smoking marijuana just like they treat alcohol: Don’t smoke and drive,” he said.
The data was presented as an abstract at the ACS Clinical Congress Scientific Forum.
