Start vaping — and you could be moving on to the harder stuff real soon.

A new study finds that among young adults who didn't smoke cigarettes, the ones who had used electronic cigarettes were more than four times as likely than nonvaping peers to start smoking traditional tobacco cigarettes within 18 months.

Almost half of the participants in the study who were vaping later began using regular cigarettes for the first time, according to the findings published Monday in the American Journal of Medicine.

The research, from the University of Pittsburgh, come as e-cigarettes are being touted as a less harmful alternative to smoking tobacco cigarettes, which are known to cause cancer. E-cigarettes deliver users a dose of nicotine in aerosol form, instead of from smoke that is the result of combusted tobacco.

Dr. Brian Primack, director of Pitt's Center for Research on Media, Technology and Health, said the results were surprising.

He noted that the average age of initiation for tobacco smokers is 11.2 years old. The new study, Primack said in an interview with CNBC, suggests that the practice of vaping could turn someone much older than that who would not otherwise be a cigarette smoker into one.

"By the time someone has turned 18 and has never touched a cigarette, it would be very unlikely [otherwise] that the person would be starting to smoke cigarettes anytime soon," he said.