When teenagers drink, it's all too often all out, downing five or more beers in a session. But some teenagers are drinking even more, a study finds, boosting the upper limits of binge drinking to 15 drinks or more.

In a poll of high school seniors, 20 percent said they'd had five or more drinks in a row in the past two weeks. That's what health officials consider binge drinking.

But 10 percent said they'd had 10 or more drinks at a time, and 5.6 percent said they'd had 15 or more drinks.

Drinking at that level would produce blood alcohol levels four to five times the legal limit for an adult. The risks of serious injury through driving or other accidents, or death due to alcohol poisoning are dramatically higher.

Earlier national surveys haven't asked about extreme binge drinking, says Megan Patrick, a research assistant professor at the University of Michigan and lead author of the study. "We've had these high rates of emergency room use from underage alcohol use," Patrick told Shots. "This helps explain it."

In 2005, questions about drinking more than five drinks in a row were added to the study, a federal survey of adolescent behavior. Now there's enough data to say that the numbers are reliable, Patrick says. (Though the study notes that at these extremely high levels of alcohol consumption, drinkers' memories may be a bit impaired.)

"Fifteen drinks in a row is a lot for anyone," Patrick says. "Remember, we're talking about 18-year-olds. It's very serious."

The survey data, reported online in JAMA Pediatrics, ran from 2005 to 2011, and involved more than 16,000 high school seniors.

Young men were more apt to say they binge drink than young women, and white students were more likely binge drinkers than ethnic minorities at the lower levels — but once it got up to 15 drinks or more, all ethnic groups were equally susceptible. Students with more educated parents were more likely to binge at the 5- and 10-drink levels, but not at 15-plus. Students in rural areas were more likely to indulge in extreme binge drinking.

In 2011, 70 percent of 12th-graders said they had had a drink at least once in their lives, and 51 percent said they had gotten drunk. Those rates are similar to or less than those in other Western countries, the researchers say.

Teen drinking rates have declined since the 1970s, but the rates of extreme binge drinking have remained stubbornly high.

Prevention efforts have been focused on binge drinking at the 5-drink level, an accompanying editorial notes, not at the extreme levels reported here. Researchers need to start asking about extreme drinking routinely, the editorial says, so that scientists can figure out what kinds of interventions will help reduce this high-risk form of alcohol use.

And that's not to say that downing five drinks a night is OK; because so many teenagers are often drinking to that level, the risk of harm from "light" binge drinking is major, too.

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