Effect of cannabis use on cognitive functions and driving ability

Neither experimental nor epidemiologic approaches have so far given definitive answers to the question of the potential effect of cannabis on driving ability.

To shed more light on this topic, we conducted a placebo-controlled double-blind study including 60 healthy volunteers (a negative urine drug screening test was prerequisite). On the first day, baseline data were obtained from a physical examination and a psychological test battery for the investigation of visual and verbal memory as well as cognitive perceptual performance. On the second day, subjects received a regular cigarette or one containing 290 microg/kg body weight of tetrahydrocannabinol. Physical and psychological assessments were performed immediately (15 minutes) after subjects smoked their cigarettes. Twenty-four hours later, physical and psychological examinations were repeated.

Our results suggest that perceptual motor speed and accuracy, 2 very important parameters of driving ability, seem to be impaired immediately after cannabis consumption.