Friday, December 2, 2011

Marijuana Use May Double the Risk of Accidents for Drivers

Marijuana Use May Double the Risk of Accidents for Drivers

Last week I discussed the issue of talking to teens about medicinal marijuana and the harmful effects of smoked marijuana. Since most teens are very interested in driving, a discussion of the risk of accidents may be helpful.
A recent meta-analysis by Columbia University's Mailman School of Public Health[1] examined the link between marijuana use by drivers and risk of a car accident.
The 2009 National Survey on Drug Use and Health estimated that over 10 million people age 12 or older had driven under the influence of illicit drugs in the prior year. 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, the 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 frequency of self-reported marijuana use.
8 of 9 studies found that drivers who use marijuana are significantly more likely to be involved in crashes than drivers who do not. The analysis indicates that 28% of fatally injured drivers 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 driving safety and public policy. It also would play a critical role in informing policy on the use of medical marijuana."
While education can be helpful in pointing out risk factors to teens, it is important to remember that teens may experience a sense of invulnerability or “optimism bias” whereby they feel that they would avoid negative outcomes. Therefore, multi-pronged approaches including social norming campaigns and publicized penalties for drugged driving behaviors are more likely to have an impact on behavior than education alone.

[1] M.-C. Li, J. E. Brady, C. J. DiMaggio, A. R. Lusardi, K. Y. Tzong, G. Li. Marijuana Use and Motor Vehicle Crashes. Epidemiologic Reviews, 2011; DOI: 10.1093

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