Teens who vape—use an e-cigarette—were almost three times more likely to have started smoking tobacco cigarettes a year later than those who had never vaped, according to a recent study in the journal Tobacco Control.

“That’s worrying news,” says Consumer Reports chief medical adviser Marvin M. Lipman, M.D. “Although the long-term safety of e-cigarettes and other nicotine vaporizers is still unknown, there’s no question that nicotine in any form is an extremely addictive drug and that tobacco products can be deadly,” he says.

To find out how vaping affected teen’s cigarette smoking habits, researchers from the University of Hawaii Cancer Center asked 2,338 9th and 10th graders at six Hawaiian high schools in 2013 about their vaping and smoking habits. One year later the scientists quizzed the teens again. The upshot: 20 percent of the e-cigarette-using teens had started smoking traditional cigarettes. By contrast, 2 percent of the non-vapers had started smoking tobacco cigarettes, 10 percent had tried vaping, and 4 percent were both smoking and vaping.

The study also found that teens who were heavier users of e-cigarettes were more likely to become regular cigarette smokers a year later. And for those who already smoked cigarettes, e-cigarettes did not help them quit smoking, contradicting the popular argument that vaping leads to a reduction in smoking.

Earlier studies have arrived at similar conclusions. For example, a  study of 40,000 middle- and high-school students published in 2014 in the journal JAMA Pediatrics found that smokers who also used e-cigarettes tended to smoke more than smokers who didn’t use e-cigs. And in October 2015 the U.S Preventive Services Task Force, an independent panel of experts that advises the government on health issues, decided not to recommend e-cigarettes as smoking cessation devices.

“E-cigarettes and other liquid nicotine vaping devices come in a variety of sweet-smelling and tasting flavors, such as bubblegum, cherry, gummy bear, and watermelon, which are clearly designed to appeal to teens,” Lipman says, “and once teens are hooked on nicotine, studies like this one suggest that teens frequently graduate from vaping to smoking regular cigarettes—creating a new generation of smokers with all the associated health risks, including heart disease and cancer.”