Dagga ups road accident risks
2005-12-02 10:06
Paris - Driving after smoking a joint roughly doubles the risk of a fatal car crash, although cannabis' share in lethal road accidents remains far behind that of alcohol, a study says.
Researchers evaluated 10 748 fatal car accidents in France that had taken place between October 2001 and September 2003, and whose drivers had been tested for drug and alcohol levels.
They compared the 6 766 drivers deemed at fault for the crash with the other drivers who were considered blameless.
Cannabis was clearly linked with fatal accidents, with the risk rising as the concentration of delta-tetrahydrocannabinol (THC), the drug's active ingredient, increased in the blood.
The odds ranged from 1.89 (almost double the risk) for a concentration of less than one nanogramme of THC per millilitre of blood, to 3.06 (more than triple the risk) for more than five ng/ml.
Samples showed that the prevalence of cannabis in France's driving population is 2.9%, roughly the same as for illegal levels of alcohol, in which 2.7% of those tested were above the legal limit of 0.5 grammes of alcohol per litre of blood.
Alcohol, though, plays a far bigger role in fatal car crashes, accounting for 28.6% compared to around 2.5% for cannabis.
The study, which appears in Saturday's issue of the British Medical Journal, is led by Bernard Laumon of the French National Institute for Transport and Safety Research (Inrets).