The issue here goes to longevity of use. The Clinical Data on the baseline product that was used---that being Nicotrol is straight forward and very well spelled out:
Originally Posted by markarich159
Nicotine from any source can be toxic and addictive... the risk of nicotine replacement in a smoking cessation program should be weighed against the hazard of continued smoking, and the likelihood of achieving cessation of smoking without nicotine replacement
Sustained use (beyond 6 months) of NICOTROL NS by patients who stop smoking is not recommended and should be discouraged
. The clinical findings is not for extended use of the product beyond six months .
It can be readily scene that the use of NRT
's balances the harm to the benefit and that the use of these products is not for an indefinate period of time like the e-cig. So it is that not that the clinical trials of approved drugs like Nicotrol dismissed the carciniginic by-products, rather they weighted the risk to benefit for short term use of these products in an effort to get the patient off of cigarettes.
On the otherhand the e-cig is marketed for an "indefinate use" time and hence must withstand the scrutinity of these by-products being induced over a long period of time by human consuption.