Again, it depends on what it contains. And again, I don't think there's been a comprehensive evaluation of this. Certainly, the paper from the WHO explored some of the concerns around hazards of it. Nicotine itself, as we mentioned earlier, is quite toxic. If taken in doses of significant quantity, it can be fatal. As far as we know early on, the propylene glycol constituents seem to be an irritant to the airways and may cause problems for asthma and other things. But again, in order to be able to say with comfort or clarity that this is an acceptable risk, we need to have properly designed studies that demonstrate efficacy as well as a well-characterized frequency of adverse events.
On October 21st, 2014. See this statement in context.