I haven't heard of any studies on VG but it's generally regarded as completely safe. There have been limited studies on PG, and it seems it may actually be beneficial to peoples health from what I've read; In one study they gave one half of rodents PG and one half nothing and then starved all the rodents of oxygen. The rodents who were given the PG fared better than the other ones. They decided that PG could potentially be used as a preventative measure in people who are at risk for stroke. (since stroke causes a part of your brain to be deprived of oxygen-you might fare better after a stroke if you had PG in your system first) IN another study they gave half the rodents PG and half the rodents nothing, then they put all the rodents in a box with some fancy rodent flu virus. The rodents who had the PG first didn't get the flu but the rodents who didn't get the PG all got the flu. At one time the government was considering having PG pumped into the schools to cut down on the incidents of flu outbreaks among children. Why the FDA wants to shut us down but still keep cigarettes on the market is absolutely bizarre to me.