A new study has found that cannabis edibles can significantly impair driving ability for several hours after consumption. Researchers who administered varying doses of THC-infused gummies to regular cannabis users observed notable declines in driving performance, particularly at higher doses.
The study, published Monday in JAMA Network Open, involved 40 adult participants aged 19 to 45 who regularly used cannabis for nonmedical purposes. Subjects were given either placebo gummies or edibles containing THC doses of 2, 10, or 20 milligrams before operating a driving simulator. While a 2-milligram dose did not show a meaningful effect, those who consumed 10 milligrams demonstrated increased lane weaving compared to the placebo group. At 20 milligrams, participants exhibited slower reaction times and inconsistent speeds in addition to impaired lane keeping.
Lead author Dr. Bernard Le Foll, a senior scientist at the Center for Addiction and Mental Health in Toronto, emphasized the severity and duration of the impairment. “Drivers were affected two hours after ingestion and remained impaired five hours later,” he said, noting the prolonged nature of the effects. He also remarked on the common misconception among users that cannabis might enhance driving, cautioning that the data clearly show otherwise.
The research focused on a relatively straightforward driving scenario, simulating rural road conditions, and the authors noted that results could differ in complex urban environments or among different populations, such as younger or older adults or medical cannabis users.
Cannabis edibles have grown in popularity amid expanding legalization of recreational marijuana, with doses under 2.5 milligrams typically considered low and nonintoxicating. Psychoactive effects generally begin at around 5 milligrams. Experienced consumers often take 10 milligrams, while 20 milligrams is regarded as a high dose.
The study builds on limited existing research regarding cannabis edibles and driving. Another recent investigation examined combined effects of low doses of cannabis edibles and alcohol, finding that their joint use produced impairment equivalent to a blood alcohol concentration of 0.08 percent—the legal limit for driving in many jurisdictions. That study observed some impairment from 10 milligrams of THC alone, though this did not reach statistical significance.
An editorial accompanying the new study, authored by José Ignacio NaziF-Munoz of Université de Sherbrooke, highlighted the delayed onset and extended duration of edible-induced impairment. He warned that because edibles do not cause immediate intoxication, users may unknowingly drive while impaired hours after consumption.
The study also found that impairment occurred at blood THC concentrations below legal limits adopted by some states, complicating law enforcement efforts. Unlike blood alcohol content, which closely correlates with impairment levels, blood THC levels are a poor indicator of current impairment, sometimes appearing when a person is not impaired or lingering after effects have subsided.
Experts stress the need for greater public awareness of the risks posed by cannabis edibles when driving and caution that current legal frameworks may not adequately address these challenges.