All of your friends probably think that smoking e-cigarettes is much healthier than smoking actual cigarettes. This is something that’s become pretty common knowledge, especially among teenagers. But even though it may be healthier overall, new research published in The Journal of the American Medical Association shows that high school students who smoke e-cigarettes are more likely to start smoking tobacco over the next year — suggesting it might be better to avoid starting in the first place.

Researchers from the University of Southern California, Los Angeles found that students who reported smoking e-cigarettes were more likely to report smoking a combustible tobacco product at a six- and 12-month follow-up. This result held even after adjusting for sociodemographic, environmental, and intrapersonal risk factors. Combustible tobacco is generally classified as cigarettes, cigars, and hookah, all of which have well-known negative health consequences. Currently, conventional tobacco use is the leading cause of preventable death and disability in the U.S.

“These data provide new evidence that e-cigarette use is prospectively associated with increased risk of combustible tobacco use initiation during early adolescence,” the authors wrote in the study. “Associations were consistent across unadjusted and adjusted models, multiple tobacco product outcomes, and various sensitivity analyses.”

The study included 2,530 students from 10 different high schools in Los Angeles, and whose average age was 14. Each one of them reported never having used combustible tobacco at the beginning of the study. During a six- and 12-month follow-up, each was asked to report whether they had used combustible tobacco products.

Without federal regulations to control the sale of e-cigarettes to minors, companies are not only able to market their products to young people, but they’re also able to ride on the widespread belief that e-cigarettes aren’t as harmful or addictive as real cigarettes.

Estimates from the Monitoring the Future Study show that in 2014, 16 percent of 10th graders reported using e-cigarettes, 43 percent of whom had never tried a combustible tobacco product. Meanwhile, a recent study found evidence that e-cigarettes might be safer than tobacco products, but they’re not any less addictive. That said, the study sheds light on how e-cigarettes may not be as harmless as most people think, and may even stoke calls for more regulation of the e-cigarette industry, which sold as much as $2 billion in products last year.

Source: Leventhal A, Strong D, Kirkpatrick M, et al. Association With Electronic Cigarette Use With Initiation of Combustible Tobacco Product Smoking in Early Adolescence. The Journal of the American Medical Association. 2015.