Pot use may nearly triple crash risk

Drivers who have been smoking marijuana are more than twice as likely as other drivers to crash their vehicles, according to research published this month in Epidemiologic Reviews. And if they've been drinking alcohol, as well, the risk climbs higher.

That might have implications in states that allow medical use of marijuana, said study senior author Dr. Guohua Li, a professor of epidemiology at Columbia University Mailman School of Public Health in New York City.

The study notes that 16 states and the District of Columbia have passed laws to decriminalize marijuana for medical use. "Although marijuana is the most commonly detected nonalcohol drug in drivers, its role in crash causation remains unsettled," they wrote.

The researchers looked at nine earlier studies published in English in six countries that focused on marijuana use in motor vehicle crashes. All but one of them showed increased risk of crashes when the driver used marijuana. That one, from Thailand, was small, they said.

One of the studies said driving skills suffer for three or four hours after marijuana use.

Using a "random effects model," the researchers calculated the overall odds of a crash at 2.66 times higher than for those who were not using marijuana.

They said the heightened risk of crash involvement associated with using pot persisted after they adjusted for confounding variables and it increased based on the amount of marijuana used and the frequency.

"This meta-analysis suggests that marijuana use by drivers is associated with a significantly increased risk of being involved in motor vehicle crashes," the researchers wrote.

An article in USA Today on the research noted that "a large U.S. survey in 2009 estimated that more than 10 million people aged 12 and over had driven while under the influence of illicit drugs in the previous year. And testing has revealed that 28 percent of drivers who die from a crash and more than 11 percent of drivers in general test positive for drugs other than alcohol. Marijuana is the most commonly detected drug in drivers after alcohol."

It could be a problem among the young, as well. A study published earlier this year in the Journal of Addiction Medicine found that 4 in 10 high school students have tried marijuana and more than 30 percent have used it in the past year.

Among the problems associated with heavier marijuana use cited in that research were poorer sleep, breathing issues, learning, memory and attention deficits, poor school performance and a higher likelihood of dropping out.

With the new research, experts told USA Today that marijuana may increase the risk of crashes because it could interfere with reaction times and coordination, among other things.

Authors of the new study said research must look at the crash risk and whether it changes with different doses, strengths and methods of using pot. And they pointed out that none of the studies they examined looked specifically at medical marijuana.

USA Today said one expert "cautioned against inferring too much from this study, which was not designed to capture cause and effect."

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