Effect of cannabis use on cognitive functions and driving ability.

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

Method: 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.

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