Products with tetrahydrocannabinol (THC) have become legal in more places in recent years, but a new study demonstrates how it is still important to use caution when taking them. The research found that more than 40% of drivers who died in motor vehicle collisions over the past six years tested positive for THC.
Specifically, the research team led by professor of surgery Akpofure P. Ekeh of Wright State University in Dayton, Ohio, found that these crash victims had active delta-9-tetrahydrocannabinol in their system. This is the part of the marijuana or cannabis plant that produces a “high” for users.
Fatal motor vehicle accident victims often had levels of THC “far exceeding those considered to cause impairment,” of around 2 to 5 nanograms per milliliter (ng/mL), according to the research. It was presented during the American College of Surgeons (ACS) Clinical Congress 2025, held in Chicago from last Saturday through this Tuesday.
Ekeh’s team analyzed coroner records from Montgomery County in Ohio dating from January 2019 to September of last year to conduct the study – a period that includes the states legalization of recreation cannabis in 2023.
They focused on 246 deceased drivers who were tested for THC following a fatal crash.
“I was surprised to see that level,” Ekeh said. “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.”
This isn’t the first time that the ACS has run alarm bells about cannabis use and driving. In 2018, it issued a warning about cannabis and called it one of the “most commonly abused substances in the U.S.” Furthermore, it said that it was “one of the most commonly detected intoxicants in driving-related incidents.”
According to that ACS press release, active components in cannabis “increased almost sixfold in content and potency,” over the past three decades as its use also increased.
Last January, Audacy reported on lawmakers in Washington and Vermont who were concerned about high potency cannabis. Both of those states are among the 24 in the U.S. that have legalized small amounts of cannabis (marijuana) for adult recreational use, along with two territories and the District of Columbia, according to the National Conference of State Legislatures. Other states also have more limited legalization of marijuana, including allowances for medical uses.
Facts about marijuana published this summer by the Pew Research Center indicate that more than half (51%) of U.S. adults have tried marijuana at some point. Based on data from 2023, 23% of adults said they had used marijuana in the prior year, while 16% had used it in the prior month.
Data from the recent study in Ohio found that 103 drivers (41.9%) overall tested positive for THC, with yearly rates ranging from 25.7% to 48.9%. Legalization did not appear to impact the rate of drivers who tested positive for THC.
“The research highlights a significant and persistent public health risk that is unchanged by the legalization of recreational cannabis, the authors said,” said a press release from the ACS.
Per the U.S. Drug Enforcement Administration, there have been no reported marijuana overdose deaths. However, that doesn’t mean taking the drug isn’t associated with risks. For example, the DEA also said there have been an increasing number of emergency room visits associated with “edibles” containing THC.
“The messaging over the last few years has been just the push towards recreational legalization,” Dr. Ekeh said. “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.”