Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study

Abstract Aim: We conducted a responsibility analysis to determine whether drivers injured in motor vehicle collisions who test positive for Δ‐9‐tetrahydrocannabinol (THC) or other drugs are more likely to have contributed to the crash than those who test negative. Design: Prospective case–control study. Setting: Trauma centres in British Columbia, Canada. Participants: Injured drivers who required blood tests for clinical purposes following a motor vehicle collision. Measurements: Excess whole blood remaining after clinical use was obtained and broad‐spectrum toxicology testing performed.