Marijuana's effects on actual driving performance were assessed in a series of three studies wherein dose-effect relationships were measured in actual driving situations that progressively approached reality. The first was conducted on a highway closed to other traffic. Subjects were treated on separate occasions with THC 100, 200 and 300 microgram per kilogram, and placebo. They performed a 22-km road tracking test beginning 30 and 90 minutes after smoking. Their lateral position variability increased significantly after each THC dose relative to placebo in a dose-dependent manner for two hours after smoking. The second study was conducted on a highway in the presence of other traffic. Subjects were treated with the same THC doses as before. They performed a 64-km road tracking test preceded followed by 16-km car following tests. Results confirmed those of the previous study. Car following performance was only slightly impaired. The third study was conducted in high-density urban traffic. Separate groups of 16 subjects were treated with 100 microgram per kilogram THC and placebo; and, ethanol and placebo. Alcohol impaired performance relative to placebo but subjects did not perceive it. THC did not impair driving performance yet the subjects thought it had. These studies show that THC in single inhaled doses up to 300 microgram per kilogram has significant, yet not dramatic, dose-related impairing effects on driving performance. (A)
Samenvatting