The role of alcohol as a major factor in motor vehicle crashes is well established.
Much less information is available concerning the contribution of other drugs.
Many legal and illegal drugs other than alcohol can impair driving ability, even in moderate concentrations, and may increase crash risk. However, their use among drivers is apparently quite limited, and there is presently insufficient scientific evidence that any drug other than alcohol increases crash likelihood. There is not much information on drug use among drivers or on driver impairment by drugs other than alcohol. Information on drivers' drug use comes primarily from tests on people killed in crashes or hospitalized with crash injuries. Also, drugs other than alcohol are infrequently found alone.