A study by the French National Institute for Transport and Safety Research published in the British Medical Journal found that seven percent of drivers involved in a fatal highway crash used marijuana.
The researchers estimated that at least 2.5 percent of the 10,748 fatal crashes studied were directly caused by the use of marijuana.
The researchers concluded that the risk of being responsible for a fatal crash increased as the blood concentration of THC, the active ingredient in marijuana, increased. Even small amounts of marijuana could double the chance of a driver suffering an accident, researchers said, and larger doses could more than triple the risk.
The number of highway deaths contributed the smoking pot were significant, even though they were dwarfed by the number caused by drinking alcohol. Of the drivers involved in fatal accidents, 21.4 percent tested positive for alcohol consumption. Alcohol was estimated to be responsible for 28.6 percent of all fatal highway accidents.
The French research found that 2.9 percent of drivers involved in fatal crashes tested positive for both marijuana and alcohol. Men were more often involved in fatal crashes than women and were more often tested positive for both marijuana and alcohol.
Totally IrresponsibleYoung drivers and drivers of motorcycles and mopeds were also more likely to test positive for both substances.
"Research like this proves just how dangerous it is to take drugs, and then get behind the wheel of a car," Roger Vincent, of the Royal Society for the Prevention of Accidents, told the BBC. "It is totally irresponsible, as taking drugs such as cannabis does affect your reactions."
Source: The study was published in the Dec. 3, 2005 issue of the British Medical Journal.