Teens who used non-cigarette tobacco products were twice as likely to begin smoking cigarettes within a year of use, according to a newly published analysis of data.

The cigarette uptake rate at one-year follow-up was four times higher among adolescents who used more than one non-cigarette tobacco product, researchers from the University of California, San Francisco’s Center for Tobacco Control Research and Education wrote in JAMA Pediatrics, published online Jan 2.

More than a dozen recent studies have linked teen use of electronic cigarettes and other non-cigarette tobacco products with cigarette smoking uptake, and UCSF researcher Shannon Lea Watkins, PhD, said the evidence that they raise the risk for adolescent smoking is now indisputable.