Study Confirms Cannabis Edibles Impair Driving for Hours, Even at Low Blood THC Levels

A peer-reviewed randomized clinical trial published August 31, 2026, in JAMA Network Open found that THC edibles impair simulated driving performance in a dose-dependent manner, with effects persisting at least five hours after consumption. Researchers at the Centre for Addiction and Mental Health in Toronto tested 40 regular cannabis users (ages 19-45) with commercially available gummies delivering 0 mg, 2 mg, 10 mg, or 20 mg of THC. Key findings included significantly increased standard deviation of lateral position (SDLP)—a measure of lane weaving—at the 10 mg and 20 mg doses two and five hours post-ingestion, along with elevated speed variability and reaction times, particularly at the highest dose. Peak whole-blood THC concentrations reached only 3.4 ng/mL at 20 mg, falling at or below common U.S. per se enforcement thresholds of 1-5 ng/mL. Participants also reported reduced willingness to drive in a dose-dependent fashion. The study, funded by Public Safety Canada, aligns with prior simulator research from the University of Colorado Anschutz and a Johns Hopkins trial showing edibles combined with alcohol produce greater impairment than either substance alone. Coverage in The New York Times and MedicalXpress highlighted the prolonged effects and mismatch between subjective feelings of sobriety and objective performance deficits. Similar patterns appear in earlier meta-analyses and Canadian studies on edibles, underscoring risks for daily drivers as edible use rises with legalization.