Drivers who ate THC edibles showed measurable driving problems even when their blood tests stayed below a commonly used legal threshold, according to Fox News’ summary of a study published in JAMA Network Open.
What the study tested
Per Fox News, researchers at the Centre for Addiction and Mental Health (CAMH) in Toronto ran a driving-simulator trial with 40 healthy adults who regularly use cannabis. Each participant completed four sessions, consuming gummies with 0, 2, 10, or 20 milligrams of THC. Performance was tested at 2, 5, and 24 hours after ingestion. Blood samples and self-reported intoxication were also collected.
What researchers observed
Fox News reports the study found impairment at 2 and 5 hours after 10 mg and 20 mg doses. Compared with placebo, participants had greater variability in lane position; at 20 mg, they also reacted more slowly and kept speed less consistently.
Average peak blood THC concentrations were reported as 1.6 ng/mL after 10 mg and 3.4 ng/mL after 20 mg—below a commonly used 5 ng/mL cutoff, though Fox News notes thresholds vary by jurisdiction and some individual samples exceeded 5 ng/mL.
Participants also said they were less willing to drive and felt less confident in their driving after taking the gummies, according to Fox News.
How edibles differ from smoking
Fox News contrasts the edible findings with the team’s previous smoked-cannabis study: drivers with similar impairment had an average peak blood THC concentration of 30.3 ng/mL—nearly 10 times higher than the 20 mg edible group’s average peak.
Enforcement challenge flagged in commentary
In an accompanying commentary cited by Fox News, Dr. José Ignacio Nazif-Muñoz of the Université de Sherbrooke wrote that edible cannabis’ delayed absorption and prolonged effects complicate interpreting biological measures for roadside enforcement. “The delayed absorption and prolonged duration of effects of edible cannabis distinguish it from smoked or inhaled cannabis, complicating the interpretation of biological measures,” he wrote.
Limits and lingering effects
Fox News notes the trial used a simulator, not on-road testing, and focused on regular cannabis users, leaving questions about occasional users. At 24 hours, residual effects were minimal: maximum speed remained slightly higher after 10 mg and 20 mg doses, but self-reported intoxication had faded, according to Fox News.
Attribution: All findings and quotes above are reported by Fox News from a study published in JAMA Network Open and related commentary.
Editor’s note: Human review and approval are required before publication.
