Cannabis edibles impair driving even when blood THC levels are low

A clinical trial published in JAMA Network Open indicates that cannabis edibles can significantly impair driving performance even when blood THC levels remain below standard legal limits used for roadside enforcement.

Researchers at the Centre for Addiction and Mental Health in Toronto conducted a randomized, double-blind study involving 40 regular cannabis users. Participants consumed THC gummies in doses of 2, 10, and 20 milligrams. The study found that those consuming 10mg and 20mg doses experienced impaired lane control and slower reaction times at two and five hours after consumption.

Crucially, the blood THC concentrations for these impaired drivers averaged between 1.6 ng/mL and 3.4 ng/mL, which is below the 5 ng/mL threshold used in several jurisdictions to determine impairment. This suggests that current per se THC limits, which were largely developed based on inhaled cannabis, may fail to detect impairment caused by the slower absorption and longer duration of oral consumption.