More teens are trying out e-cigarettes than the real thing, according to the government's annual drug use survey.

Researchers were surprised at how many 8th, 10th and 12th graders reported using electronic cigarettes this year, even as regular smoking by teens dropped to new lows.

Nearly 9 percent of 8th graders said they had used an e-cigarette in the previous month, while just 4 percent reported smoking a traditional cigarette, said the report being released Tuesday by the National Institutes of Health.

Use increased with age: Some 16 percent of 10th graders had tried an e-cigarette in the past month, and 17 percent of high school seniors. Regular smoking continued inching down, to 7 percent of 10th graders and 14 percent of 12th graders.

"I worry that the tremendous progress that we've made over the last almost two decades in smoking could be reversed on us by the introduction of e-cigarettes," said University of Michigan professor Lloyd Johnston, who leads the annual Monitoring the Future survey of more than 41,000 students.

The survey didn't ask about repeat use, or if teens were just experimenting with something new. But between 4 percent and 7 percent of students who tried e-cigarettes said they'd never smoked a tobacco cigarette, noted University of Michigan professor Richard Miech, a study senior investigator.

"They must think that e-cigarettes are fundamentally different," he said.

E-cigarettes often are described as a less dangerous alternative for regular smokers who can't or don't want to kick the habit. The battery-powered devices produce vapor infused with potentially addictive nicotine, but without the same chemicals and tar of tobacco cigarettes.

E-cigarettes began to appear in the U.S. in 2006, but this was the first year that the Monitoring the Future survey asked teens about them. The Centers for Disease Control and Prevention has estimated that during 2013, 4.5 percent of high school students had tried e-cigarettes during the prior month, a tripling since 2011.

The CDC reported last week that 10 states permit the sale of e-cigarettes to minors. The Food and Drug Administration has proposed regulating e-cigarettes, including banning sales to minors; there is no timetable for final rules.

Other findings from the survey, funded by NIH's National Institute on Drug Abuse:

—Marijuana use appeared to level off after recent increases, with 6.5 percent of 8th graders reporting past-month use, 17 percent of 10th graders and 21 percent of 12th graders. Nearly 6 percent of 12th graders reported daily use.

—Fewer teens are trying synthetic marijuana, highly dangerous drugs known by such names as K2 and Spice. About 6 percent of seniors said they had used fake pot this year, down from 8 percent last year and 11 percent in 2012.

—Abuse of prescription painkillers is dropping. Six percent of high school seniors reported using the narcotics without medical supervision in the past year, down from 9.5 percent in 2004.

—Nearly 1 in 5 12th graders reported binge drinking, defined as five or more drinks in a row in the previous two weeks. That's down from 1 in 4 high school seniors in 2009.