E-cigarettes may be a gateway device to nicotine addiction among teens, according to a recent study.

Researchers at the University of Southern California found that teens who have tried personal vaporizers are more likely to start smoking traditional cigarettes and other combustible tobacco products within the next year.

"While teen tobacco use has fallen in recent years, this study confirms that we should continue to vigilantly watch teen smoking patterns," Nora D. Volkow, director of the National Institute on Drug Abuse, said in a statement. "Parents and teens should recognize that although e-cigarettes might not have the same carcinogenic effects of regular cigarettes, they do carry a risk of addiction."

For the study, researchers collected and analyzed data from more than 2,500 14-year-olds in Los Angeles "who had tobacco never used conventional products including cigarettes," The Associated Press reported. Students were asked about lifetime and past six-month use of e-cigarettes, combustible cigarettes, full-size cigars, little cigars/cigarillos, hookah water pipes, and blunts.

They were surveyed six months later and again at the start of 10th grade.

Of the 9 percent of the student surveyed -- 22 percent -- said they had vaped in the past, and six months later, about a third of them said they had also tried a "traditional tobacco product," such as a cigarette or a cigar, NBC News reported. Only 8 percent of the kids who never tried e-cigarettes had used a tobacco product.

A year later, participants were surveyed again. This time, 5 percent of them who admitted to vaping said they'd also smoked tobacco in the past 6 months, compared to 9 percent of non-vapers.

"While we cannot conclude that e-cigarette use directly leads to smoking, this research raises concerns that recent increases in youth e-cigarette use could ultimately perpetuate the epidemic of smoking-related illness," Adam Leventhal, who led the study, told NBC News. "Adolescents who enjoy the experience of inhaling nicotine via e-cigarettes could be more apt to experiment with other nicotine products, including smokeable tobacco."

The authors recommend further studies to determine whether the observed link between e-cigarettes and smoking initiation is causal.

The findings are detailed in the Journal of the American Medical Association.