Hi tsalis and welcome to ECF. As others have mentioned there has been no real clinical trials in which the effect of vaping were studied. I can tell you that The Doctors TV Show recommends the Ecig
Electronic Cigarette-ecigarette: Featured on The Doctors TV Show. - YouTube
The AASPS (Association of American Physicians and Surgeons) also has a petition for Doctors promoting the use of the Ecig and have stated PG and VG are safe to use in Ecigs.
AAPS - Association of American Physicians & Surgeons
As for my own personal experience my Doctor, Dentist and Nose Surgeon all support my use of the Ecig and have encouraged me to vape in their offices in the hopes that other patients/ smokers will try it.
In regards to PG/ Propylene Glycol:
Medical Uses
PG has been used as the aqueous-based chemical additive in asthma inhalers and nebulizers since the 1950s, with no serious side effects known. PG, because of its water-retaining properties, is the compound of choice for delivering atomized medication. It is also a common diluent for injectable medications, constituting 40 percent of the intravenous form of Phenytoin, an anti-seizure drug.
Electronic Cigarettes
Persons trying to quit smoking have recently turned to the recent invention of electronic cigarettes. Battery-powered, these devices deliver measured amounts of nicotine diluted in PG and then inhaled. A heating element within the device vaporizes the compounds, thereby allowing for easy inhalation. While many have questioned the safety of electronic cigarettes, their concerns are directed toward the inconsistent amounts of nicotine, not the PG solution in which it is delivered.
There is a Doctor in Alberta Canada that is studying Ecigs. He supports the use of Ecigs and stated his only concern was Quality Control. He also stated his testing indicated ALL Ecig companies operating in North America were delivering their product as advertised and Quality Control was not an issue.
Of course there are no long term clinical trials so we just have to go by little bits and pieces here and there. The success rate of Ecigs is far greater than other cessation forms/ methods.
Personally I know if I continue to smoke I will either die or have serious health issues. While the risk from Ecigs are relatively unknown I prefer to take that risk based on my own research.
Hope this helps, Vapoor.