A small study conducted at Virginia Commonwealth University concluded that e-cigarettes failed to deliver on their promise of providing a dose of vaporized nicotine with every puff, CNN reported Feb. 8.

Sixteen volunteers were given two popular brands of e-cigarettes to use; the tobacco-free devices use a battery to heat a liquid containing nicotine, which users then inhale.

However, “Ten puffs from either of these electronic cigarettes with a 16-mg nicotine cartridge delivered little to no nicotine,” according to the study led by researcher Thomas Eissenberg of the university’s Institute for Drug and Alcohol Studies, who added: “They are as effective at nicotine delivery as puffing on an unlit cigarette.”

The study, funded by the National Cancer Institute, will be published in the British Medical Journal.