LOS ANGELES (CBSLA.com) — A USC study has found that among teenagers who never smoked tobacco before ninth grade, those who had smoked e-cigarettes were far more likely to begin smoking tobacco shortly after starting high school than their peers.

The study followed about 2,500 L.A. students as they entered ninth grade.  The researchers found that six months into high school, the students who had used e-cigarettes prior to starting high school were three-to-four times as likely to begin smoking tobacco than those who had not.

The study has called into question whether e-cigs, which are not regulated by the Food and Drug Administration, are legitimate tools to help adults quit tobacco, or a gateway for teenagers to begin using tobacco. Researchers noted that some e-cig flavors, such as honey or blackberry, would be appealing to kids.

“Some of the flavors that are available could be very enticing to youths,” said Dr. Adam Leventhal, who led the study.