SAN FRANCISCO (KCBS ) — A newly released UCSF research study shows that claims made by some electronic cigarette manufacturers—that the devices actually help people quit smoking—are unlikely.

Scientists analyzed 84 research studies on e-cigarettes—battery-operated devices that vaporize a nicotine solution. They have been sold in the U.S. since the mid-2000s and have become immensely popular. They do no emit smoke, which has been part of the attraction to many, including teenagers.