A team led by Richard Miech, of the University of Michigan's Institute for Social Research, tracked the responses of nearly 15,000 students who took part in a 2015 U.S. nationwide survey.
More than 3,800 of the students -- who were in grades 8, 10 and 12 -- said they had used e-cigarettes at some point.
Of those who had used e-cigarettes within the past month, more than 1,700 had done so at least once; nearly 1,100 had done so up to five times; and more than 600 had done so more than half a dozen times, the findings showed.
Among the students who had ever used e-cigarettes, two-thirds used the device where a non-nicotine, flavored ingredient was used, the survey found.
Nicotine came in at a distant second: Used by 13 percent of 8th graders, 20 percent of 10th graders, and 22 percent of 12th graders.
Relatively few of the students tried vaping marijuana -- just 6 percent to 7 percent of all students, the study found.
The findings suggest that efforts to reduce e-cigarette use among young people may fail if they focus on the dangers of nicotine because most teen users do not believe they are using nicotine, according to the researchers.
"These results indicate that while taking into account [e-cigarette] use does indeed increase tobacco/nicotine prevalence, the impact of [e-cigarettes] is likely not as large as might appear by their recent, dramatic increase in use among adolescents," Miech and colleagues wrote.
But one expert in vaping and smoking questioned the findings.
"Although I appreciate the survey results, I question whether the adolescents actually knew for certain that what they were inhaling did or did not contain nicotine," said Patricia Folan. She directs the Center for Tobacco Control at Northwell Health in Great Neck, N.Y.
"There are nearly 500 types of vaping devices and currently the ingredients in these devices are not always known nor do they appear on the product labels," she said. "Consequently, I would have thought that there would be more teens reporting that they did not know what substances they were vaping."
Folan also believes that there's no "harmless" e-cigarette.
"Even without nicotine, inhaled products that contain flavorings can be damaging to the lung tissue and would not be considered safe for adolescents or adults," she said.
The study was published online Aug. 25 in the journal Tobacco Control.
The U.S. National Institute on Drug Abuse has more about electronic cigarettes.
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