A study published Monday in the journal Pediatrics shows an alarming new trend among teens: using e-cigarettes -- marketed by the tobacco industry as a safer alternative to traditional cigarettes -- to smoke marijuana.

In a survey conducted by Yale University researchers, nearly one in five Connecticut high school students who use e-cigarettes to vaporize nicotine also use them to vaporize cannabis. Powered by batteries, e-cigarettes turn on a heating element when you inhale that vaporizes liquid contained in small tubes in the device. They were designed to hold liquid nicotine but some teens are substituting hash oil; wax infused with THC or tetrahydrocannabinol, an active ingredient in pot; or dried cannabis leaves.

The use of e-cigarettes has been increasing rapidly among teens nationwide. In the Connecticut survey, which was conducted in the spring of 2014, 27.9 percent of high schoolers surveyed said they use e-cigarettes. Of those, 18.7 percent were "dual users," who also used the devices to vaporize marijuana.

Those who are male and younger were more likely to vaporize cannabis using e-cigarettes.

Using e-cigarettes to "vape" pot provides two advantages, said researcher Meghan E. Morean, an assistant professor of psychology at Oberlin College who conducted the study while working at a lab at Yale. One, the smell of marijuana isn't as powerful as it is when you smoke it. Second, the device provides a way to disguise what teens are really smoking.

"This is a relatively novel way of using marijuana, and kids are using it at a fairly high rate," Morean said.

In the journal article, the researchers expressed concern about the health risks related to the "increased potency of hash oil and THC-infused waxes compared to combustible cannabis."

"These findings raise concern about the lack of e-cigarette regulations," the researchers wrote in the study.

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