Cannabis Use and Car Crash Risk
A 2012 BMJ meta-analysis by Asbridge et al. found that acute cannabis consumption roughly doubles the risk of a serious motor-vehicle crash — odds ratio approximately 1.92. Subsequent NHTSA research (Hartman et al., 2021) using more rigorous toxicology methods confirmed and refined the finding, including dose-effects on lane control, reaction time, and divided-attention tasks.
A persistent myth among regular users is that "I drive fine when I'm high" — the data, however, is unambiguous. Cannabis impairs the specific motor and attention skills required for safe driving, even when subjective intoxication feels mild.
This page is a draft. The full writeup will cover the THC-blood-level cutoffs used by states with per-se DUI laws, and how cannabis impairment differs from alcohol impairment.