Abstract
Results from studies on the incidence of alcohol and drugs in road accidents show that amongst all road users, illicit drugs were present in some 16% of fatalities. Although there may be an association, this presence cannot be taken as evidence of accident causation, although recent work has reviewed the evidence of the driver impairment effects of cannabis. The paper reports on research work concerning the effects of cannabis alone, and also in combination with alcohol, on the psychomotor and cognitive skills relevant to vehicle driving.