In the DRUID (Driving under the influence of drugs, alcohol and medicines) study, the risk of injury and death was calculated for different psychoactive substances on the basis of samples collected from drivers in road traffic and in various accident situations. The number of persons having used alcohol or drugs with negative effects on the ability to drive was lower in Finland than in Europe on the average. Aggravated drunk drivers and mixed substance abusers pose an accident risk that can be several hundredfold higher compared with sober drivers. More attention should be focused on traffic risks due to mixed use of drugs and alcohol.