Sparking controversy. Rise in e-cigarette use has public health experts questioning their safety, effectiveness as harm-reduction device.

The rise of e-cigarettes in the past decade has been accompanied by a debate over the public health consequences of using the devices. Many see them as beneficial. "T'his is basically what I would call a harm-reduction strategy," says Dr. Michael Siegel, a professor of community health sciences at Boston University, comparing e-cigarette use to how methadone is prescribed to heroin addicts.