A fatal motor-car accident and cannabis use. Investigation by radioimmunoassay.

Impairment of driving skills by drugs is an important cause of traffic accidents. Alcohol is the most important, though far from the only, drug involved; and of 684 fatal accidents investigated by Woodhouse, 321 (47%) of the drivers had blood-alcohol levels greater than 100 mg/100 ml at the time of death. In 16 it exceeded 400 mg/100 ml. Unlike alcohol, cannabis has received little attention as a possible cause of traffic accidents, largely owing to the difficulty of proving cannabis use objectively. The recent development of a reliable and relatively simple method for detecting and measuring cannabis products in blood and urine may help to overcome this difficulty. As Milner has pointed out, the full effect of alcohol on driving competence was not appreciated until objective methods of measuring blood-alcohol levels became generally available. The same may be true of cannabis.