Driving under the influence of cannabis can double the odds of causing a fatal car crash and the risk increases if the drug is combined with alcohol, French scientists said today.
Researchers from the French National Institute for Transport and Safety Research (INRETS) who studied 10,748 drivers involved in fatal car crashes from 2001-2003, said about 7 percent tested positive for cannabis and 21.4 percent for alcohol.
Nearly 3 percent were under the influence of both.
"Driving under the influence of cannabis doubles, on average, the risk of being responsible for a fatal accident," said Jean-Louis Martin, a co-author of the study.
In the British Medical Journal online, the researchers said men were more often involved in crashes then women. They also tested positive more frequently for both cannabis and alcohol, along with younger drivers and people who used mopeds and motorcycles.
Although the prevalence of cannabis and alcohol among drivers was similar at about 2.8 percent, the use of alcohol was associated with many more deadly car crashes.
The researchers also found that the more cannabis smoked or alcohol consumed, the higher the chance of being involved in a fatal accident.