The findings were the result of reviewing ten separate research studies on the effects of marijuana in 49,411 auto collisions.
In a study published on BMJ.com, researchers at Dalhousie University found that drivers who smoked marijuana were twice as likely to cause an auto crash that causes serious injury or death than those not under the influence.
Risk Includes All Vehicle Types
The increase risk of marijuana use was found in the driving of cars, vans, SUVs, trucks, buses and motorcycles. The study also found that the risk of a collision is substantially higher if the driver is under age 35.
The researchers were not able to determine the impact of smoking marijuana on the risk of minor (fender bender) type crashes, from the studies they reviewed, but the increased risk was most evident in studies of fatal crashes, they said.
They also found that drivers in fatal auto crashes had a higher level of tetrahydrocannabinol (THC) in their system than those in non-fatal crashes, but that might be due to the fact that the fatal drivers' blood was tested at death while some time elapsed before drivers in non-fatal crashes were tested.
Alcohol Still More Dangerous
Although the research found that marijuana smokers were twice as likely to be involved in collisions, their study did confirm that alcohol consumption is still the No. 1 cause of vehicular crashes with drivers with a blood-alcohol level of 0.08 being 2.69 times more likely to be involved in a serious crash than those not under the influence.
Just because drinking and driving is more dangerous than smoking weed and driving, does not mean marijuana use and driving is safe, the researchers said. Pot smokers are significantly more likely to get into a collision than non-smokers.
The February 2010 BMJ study seems to confirm a previous British report by Coroner's Society president Hamish Turner which said "Marijuana Causes Many Deaths Reported as 'Accidents'," in which he said that, although smoking marijuana did not directly cause fatalities, that it was a factor in many types of accidents that were fatal.
More Than Driving Skills Affected
The distinction between marijuana causing death and being a factor in deadly accidents was apparently lost on the more than 400 stoners who posted comments calling the article a bunch of bull and the writer of the article an idiot.
Ironically, those who commented from the viewpoint that the article said "Marijuana Causes Death," when in fact the article said "Marijuana Causes Accidents," provided additional evidence that smoking weed obviously impairs more functions than mere driving skills.
Particularly humorous were the posters who claimed to have 4.0 grade-point averages or post-graduate degrees, whose comments were riddled with spelling and grammatical errors.
Source: Asbridge, M, et al. "Acute Cannabis Consumption and Motor Vehicle Collision Risk: Systematic Review of Observational Studies and Meta-Analysis," BMJ.com 9 February 2012. More About Marijuana