One of every 11 U.S. high school students says they have used marijuana in an e-cigarette, according to a nationwide survey. That equals more than 2 million teens, HealthDay reports.

Almost one-third of high school students who use e-cigarettes have vaped marijuana, according to the survey, published in JAMA Pediatrics. The survey included almost 20,700 middle and high school students from public and private schools.

“This high rate of cannabis use in e-cigarettes is a public health concern, because any form of tobacco product use is unsafe among youth, irrespective of whether it’s smoked, smokeless or electronic,” said lead researcher Katrina Trivers of the National Center for Chronic Disease Prevention and Health Promotion at the Centers for Disease Control and Prevention.