Comparison of the effects of marijuana and alcohol on simulated driving performance

We have determined the effect of a “normal social mari-juana high ” on simulated driving performance among experi-enced marijuana smokers. We compared the degree of driving impairment due to smoking marijuana to the effect on driv-ing of a recognized standard-that is, legally defined intoxica-tion at the presumptive limit of 0.10 percent alcohol concen-tration in the blood. This study focused attention on the effect of smoking marijuana rather than on the effect of ingesting a9-tetrahydrocannabinol (a9-THC), the principal active component. Weil et al. l have studied the clinical and psychological effects of smoking marijuana on both experienced and in-experienced subjects. They suggest, as do others, ’ that ex-perienced smokers when “high ” show no significant impair-ment as judged by performance on selected tests; they also establish the existence of physiological changes that are use-ful in determining whether a subject smoking marijuana is “high. ” A review of the relation of alcohol to fatal accidents3 showed that nearly half of the drivers fatally injured in an accident had an alcohol concentration in the blood of 0.05 or more. Crancer4 found a driving simulator test to be a valid indi-cator for distinguishing driving performance; this result wa