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Why do more teens report driving stoned than drunk?

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We need an MASD (Mothers Against Stoned Driving) to help convince young drivers that driving under the influence of pot is just as dangerous as driving drunk.

In a survey of 315 college freshmen from two state universities, one in five students reported using marijuana during the past month and more than half of the male students and more than one-third of the females said they rode in a car with someone who had used the drug. Nearly 44 percent of the boys and 9 percent of the girls said they drove after using marijuana, according to the study published last week in JAMA Pediatrics.

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“These findings point to a need for increased efforts to help youth understand that driving after marijuana use is risky,” said study leader Jennifer Whitehill, an assistant professor of health policy and management at the University of Massachusetts Amherst, “and they should plan a designated substance-free driver or alternate transportation.”

Perhaps they need to watch Colorado’s new “drive high get a DUI” public service announcements: One shows a man installing a TV on his wall only to have it fall a minute later. “Installing your TV while high is now legal,” reads the text in the ad. “Driving to get a new one isn’t.”

But unlike drunk driving, there is no device like a breathalyzer to test for marijuana use. To test whether drivers are high, police conduct field tests such as having a driver walk nine heel-to-toe steps or stand on one leg for 30 seconds. But a 2012 study suggests that only 30 percent of drivers who have smoked marijuana fail such a field test, compared to nearly 90 percent of drunk drivers.

“We need better methods to measure whether someone is intoxicated with marijuana,” said Dr. Nora Volkow, director of the National Institute on Drug Abuse. THC, the active ingredient in marijuana, has a long half-life and can be detected in the body for several days after a person uses the drug, even if the amounts aren’t high enough to affect their driving ability.

Researchers at NIDA are currently testing ways to accurately detect THC levels in saliva and breath tests that would indicate an impaired driver, but it is likely to take another few years before one is ready for use on the highway.

In the meantime, Colorado has seen a recent doubling in fatal car crashes involving marijuana use since legalizing the drug for medical use in 2000. Researchers from the University of Colorado School of Medicine reported last Thursday that in 2011, ten percent of fatal car crashes involved at least one driver who tested positive for marijuana compared with 4.5 percent of fatal car crashes that occurred in 1994.

While the study couldn’t prove that the drug was responsible for the crashes, it raises concerns that fatalities will increase in the state now that pot is legal for recreational use in adults over age 21.

“There’s a perception that marijuana isn’t harmful,” Volkow said, “whereas there have been very effective education campaigns to make people aware that alcohol leads to car accidents.”

In fact, the JAMA Pediatrics study found that a far lower percentage of students reported driving with someone who was drinking — or driving after drinking themselves. Only 11 percent of male students and 3 percent of female students admitted to driving under the influence of alcohol.

Part of the education campaign should include information on the latest research showing how marijuana affects a driver’s abilities. Volkow ticked off a list of findings from simulated driving tests conducted on those under the influence of marijuana: slower reaction times; difficulty estimating timing for a moving object, like a car moving toward an intersection; and inability to multi-task.

And studies also suggest that drivers who are stoned don’t feel their impairment as much as those who drive drunk.

How much time should we allow for the drug to clear our system before driving?

“At this point, we tell people if you smoke in the morning, you should not drive in evening,” Volkow said, “and it’s best to wait at least 24 hours just to be prudent. But I don’t know that we have exact data” on how long impairment actually lasts.

DEBORAH KOTZ

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.
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