According to data in the journal Drug and Alcohol Dependence, persons who consumed marijuana typically decrease their driving speed but showed few other significant changes in driving performance.
Canadian researchers evaluated the simulated driving performance of young adult subjects who had smoked a product containing high-THC, low-THC, or placebo (no THC), NORML reported. The subjects’ driving performance was analyzed 30 minutes after smoking, 24 hours and 48 hours.
“Among young regular but non-dependent cannabis users, smoked cannabis led to a significant reduction in driving speed, …but there was little evidence of residual effects,” the researchers stated.
Other studies have found similar results which suggest that cannabis consumption only slightly effects driving performance.