The major conclusion of the survey is that the common prescription drugs studied are a minor factor for the injured road accident victims. Alcohol is a major factor, affecting about 20 percent of the injured drivers. This figure is appreciably less than the 50 percent or so for the proportion of fatally injured drivers who were drinking drivers. Lack of a control group makes the interpretation of the data difficult. For example, 7 percent of the drivers were found to have been cannabis users in the few days before their accident, but the proportion of cannabis users on the road is unknown. The figure of 7 percent remains an isolated statistic. A group grossly under-reported in official statistics and with a high injury rate is motorcyclists. The victims in this group are primarily young and inexperienced; few of their accidents involved alcohol. (secondary source).
Abstract