There is no doubt that cannabis, smoked or taken by mouth produces a dose-related deficit in tests of performance skills as conducted in a laboratory. Using driving simulators and on-road real vehicles, cannabis has been shown to affect driving performance. However, the effects are less severe than would be anticipated from the evidence obtained from the laboratory studies of individual tests of skills performance. A description is given of epidemiological studies to determine the role of cannabis in road crashes. The pharmacological problems associated with these studies are described. The results of studies within the last 10 years have failed to present clear evidence for a role of cannabis in road crashes. The role of alcohol in all studies has proved to be dominant. The evidence indicates that there is a clear difference in the mode of action of cannabis and alcohol, both pharmacological and behavioural and this is presented and the implications described. (Author/publisher)
Abstract