Electronic cigarettes (e-cigarettes) are becoming increasingly popular among teens. A new study looks at whether younger teens who never smoked cigarettes and who begin using e-cigarettes might be more likely to go on to use conventional tobacco products.

Researchers from the University of Southern California, Los Angeles surveyed more than 2,300 Los Angeles area high school students who reported never using tobacco products at the beginning of 9th grade. The students were surveyed again six months later and also when entering the 10th grade.

In a comparison of teens who had used e-cigarettes to those who had not, the researchers found that those who had used e-cigarettes were four times more likely to have gone on to use conventional tobacco products, including cigarettes and cigars. The researchers acknowledge that their findings, while suggestive, cannot prove that e-cigarette use directly causes subsequent tobacco use.

Click here to read the full report on the JAMA Network.