High in cars: More high school seniors hit the road after smoking pot 

Study reports high numbers of students who drink and drive 0:17

A growing number of high school seniors are getting into cars after smoking pot, or with someone who has, a distressing trend that reflects misperceptions about the dangers of marijuana, researchers said Thursday.

An estimated 28 percent of high school seniors reported riding in a car in the past two weeks with a driver who had used drugs or alcohol, or said they had driven after using drugs or alcohol themselves, researchers found. While driving after drinking has declined in recent years, driving after use of marijuana has increased from 10 percent in 2008 to 12 percent in 2011, according to the most recent survey data from from the Monitoring the Future project, in which 17,000 high school seniors at 135 schools nationwide are interviewed every year.

“A higher percentage of students reported driving after using marijuana than after having five or more alcoholic drinks,” the researchers wrote in a report published in the American Journal of Public Health.

“It’s a big deal… the sheer numbers,” Patrick O’Malley, a research professor at the University of Michigan, told NBC News. “It has been increasing steadily and looking down the road, it seems likely to get worse. We are concerned."

The confidential questionnaires did not ask seniors about the amount of marijuana smoked, or who they got in the car with, like a parent or friends. Another problem confounding researchers is how to determine how much marijuana is too much; there is no comparable DUI standard.

“We don’t have any good degree of impairment,” O’Malley said, adding that the country remains a long way off from setting such standards. “It’s almost impossible to say what the level of marijuana in your system is.”

The study, sponsored by the National Institute on Drug Abuse, found it didn’t matter where the students lived. The increases in marijuana use were the same in four geographic regions. 

“The behavior was fairly widespread throughout society,” the researchers reported. 

O’Malley said the trend is troubling, reflecting a softening in the attitudes against marijuana that has “got to be filtering down to the kids.” Although marijuana is illegal under federal law, Washington and Colorado permit recreational marijuana use for adults and 18 states, plus Washington, D.C., allow use of medical marijuana. 

“One of the messages is that kids don’t see these things as as dangerous as they should,” he said. “It’s distressing, certainly concerning, worrying. It’s a matter we really need to pay more attention to.”

Stephen Gray Wallace, a senior adviser for Students Against Destructive Decisions, said the report only strengthened his own group’s concern.

“I’m very concerned, when you do the math, which we did," Wallace says. "That means of 13 million driving age teenagers, as many as 3 million impaired teenagers may be on the road.”

“That’s a problem,” Wallace added, particularly with the disturbing tendency of teenagers who say they don't think pot is a problem with driving.

“It’s a real call to action for parents, they need to get young people to hold the line on the legal drinking age and know what constitutes safe driving behind the wheel.”