Potency-related effects of smoked cannabis on simulated driving performance: a randomized, controlled crossover trial.
Scientific Reports March 10, 2026 Bruna Brands, Adam Zaweel, Madison Wright et al.
Smoked cannabis containing varying levels of Δ9-THC produced potency-dependent impairments in simulated driving. In a randomized, double-blind, placebo-controlled trial, adults who regularly used cannabis and held valid driver's licenses completed driving tasks after smoking placebo or cannabis with low (6.25%/47 mg), medium (12.5%/94 mg), or high (22%/165 mg) Δ9-THC. Mean speed did not differ across conditions, but maximum speed increased under medium and high potencies versus placebo. Standard deviation of lateral position (SDLP) was higher across all potencies, and reaction time (RT) was longer under medium and high potencies. Both SDLP and RT correlated positively with blood Δ9-THC concentrations. Participants reported poorer driving performance and reduced willingness to drive at higher potencies.