A smoker demonstrates an e-cigarette.

In a sign that the state is hardening its stance on electronic cigarettes, health departments throughout Tennessee are putting up posters in their buildings warning about the potential harm of the devices.

The notices caution users about e-cigs, the nicotine and other chemicals in them as well as exposure to vapor second-hand.

State health officials issued their initial advisory on e-cigs in February. Since then, the U.S. Food and Drug Administration has proposed rules calling for regulation of electronic nicotine devices.

"The additional independent research we've seen on electronic cigarettes has increased our concerns since we issued the initial advisory in February," said Dr. John Dreyzehner, Tennessee Department of Health commissioner.

"While we believe more science-based research needs to be done, Tennesseans need to have information about what is known now about how these devices can impact health."

E-cigs are battery-powered devices that heat liquid nicotine to create a vapor that is inhaled.

While the state is not conducting its own studies on "vaping," department spokesman Woody McMillan said officials are "monitoring the research of organizations from around the world and from information collected by umbrella health associations."

Research remains divided on the safety of e-cigarettes. While proponents argue that vaping provides a safer alternative to smoking cigarettes, critics are not convinced.

Currently there is no government regulation of how much nicotine or other chemical a manufacturer may put in the juice cartridges used to produce the vapors in electronic cigarettes.

Meanwhile, demand for the devices has continued to build rapidly - notably among young people.

The Centers for Disease Control and Prevention has reported that use of electronic cigarettes by students in the nation's middle and high schools has more than doubled from 3.3 percent in 2011 to 6.8 percent in 2012.

Tennessee's announcement came on the heels of the American Medical Association's decision last week to take a harder stance against e-cig companies marketing to young people.

Citing the "alarming growth in use of electronic cigarettes among minors," the national physician organization adopted new policy opposing the sales and marketing of electronic cigarettes and nicotine delivery products to minors.

Among other things, the AMA policy calls for childproof packaging, restrictions on using flavors that appeal to minors.

Contact staff writer Kate Harrison at kharrison@timesfreepress.com or 423-757-6673.