With recent changes in its legal status, the impact of marijuana on driving ability is increasingly relevant. Marijuana is the most common illicit drug reported in motor vehicle accidents (MVA) (45). However, it is difficult to ascertain a causal contribution in many of these accidents as marijuana has substantially varied effects on driving abilities due to factors such as tolerance, differences in smoking techniques, and differences in absorptions of THC (64). Evidence has shown that the potential negative effects of marijuana on driving may disappear after controlling for other risky driving behaviors (65). Epidemiological studies attempting to characterize the relationship between acute marijuana intoxication and MVA culpability have been mixed and are not as strong as the relationship between alcohol intoxication and MVAs (66).
