Marijuana use may double the risk of accidents for drivers

Over 10 million people age 12 or older are estimated to have driven under the influence of illicit drugs in the prior year, according to a 2009 National Survey on Drug Use and Health. While marijuana is the most commonly detected non-alcohol drug in drivers, its role in causing crashes has remained in question. To examine the link between marijuana use by drivers and risk of a car accident, researchers at Columbia University did a meta-analysis of nine epidemiologic studies and found that drivers who test positive for marijuana or report driving within three hours of marijuana use are more than twice as likely as other drivers to be involved in motor vehicle crashes. The researchers also found evidence that crash risk increases with the concentration of marijuana-produced compounds in the urine and the frequency of self-reported marijuana use.

According to the investigators 8 of 9 studies found that drivers who use marijuana are significantly more likely to be involved in crashes than drivers who do not. Only one small case-control study conducted in Thailand, where the prevalence of marijuana use is far lower than reported elsewhere, was the exception.

Full study findings are published online in Epidemiologic Reviews.

The analysis indicates that 28% of fatally injured and more than 11% of the general driver population tested positive for non-alcohol drugs, with marijuana being the most commonly detected substance.

Guohua Li, MD, DrPh, professor of Epidemiology at Columbia University's Mailman School of Public Health, and senior author points out that although this analysis provides compelling evidence for an association between marijuana use and crash risk, one should be cautious in inferring causality from these epidemiologic data alone. However, "if the crash risk associated with marijuana is confirmed by further research, this is likely to have major implications for and public policy. It also would play a critical role in informing policy on the use of medical marijuana."

"Given the ongoing epidemic of drug-impaired driving and the increased permissibility and accessibility of marijuana for medical use in the U.S., it is urgent that we better understand the role of in causing car accidents."

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Citation: Marijuana use may double the risk of accidents for drivers (2011, October 6) retrieved 20 October 2019 from
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Oct 06, 2011
Also, if you are a bag of doritos or a twinkie you are in great danger in the presence of a cannabis user.

I seen it on the tele...tele.....telewhatchamacallit thingie.

Oct 07, 2011
Illegal drug users tend to be people with higher inclination towards risk, more than the average person. People with more tendencies to take more risk are, of course, more at risk of car accidents.
Have they got any studies from places where marijuana use is legal and more common?
I'm sure they can do a similar study on night accidents and find that most of the drivers had drank coffee within 3 hours of accident. Does that imply that caffeine caused these accidents?

Oct 07, 2011
Correlation does not imply causation. That said it would not surprise me if marijuana use does in fact inhibit one's ability to drive somewhat. Too bad studies like this just become propaganda for prohibitionists though...

Oct 09, 2011
I think 12 is a little young to be driving.

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