This type of question as been discussed a lot on ECF. You might do some searching. I think the general consensus is that the nic in
e-liquid almost always comes from tobacco. Of course, in a cigarette it is not just nicotine that is being inhaled. So what is being inhaled between the two varies enormously. It also seems to be the case that the nic from a e-cig does not have effect on ones brain quite as fast as a cigarette. I think the belief is that cigarette nic is absorbed more in deep lungs areas whereas e-cig nic does not travel so deeply, being absorbed in mouth and higher areas of the respiratory tract. But I don't think all the facts are in on the issue. I suspect that a great deal of the variance in effect time deals with the exact method that one uses in terms or draw strength, inhale methods, exhale methods, etc. But, generally speaking, if you were a pack a day smoker of full flavor cigs, you got to your system something on the order of 2 mg of nic. (About 1 mg in a cig to start but 90% burnt up or exhausted with second hand smoke.) Since
e-liquid is rated at mg of nic per ml, a ml of 2mg e-liquid should present to your system 2 mg of nic. But what seems to be the case, 2mg of nic in e-liquid form will not work as replacement for the 2mg in the cigs. Best fit is usually obtained with trial and error. If formerly a pack a day smoker of full flavor what I have seen is the 16 or 18 mg e-liquid is somewhat common. (An usually 2 or 3 ml of it a day) But, varies widely. In my case, previously a pack to pack and half smoker, 14 or 18 mg seems the fit for me. But trial and error experience is the real test. Most would say, the lower the mg level in the e-liquid that keeps you away from the cigarettes, that is the proper level. Once the attraction to the cigarettes is gone, one can always start moving downward on the nic mg level in the e-liquid toward perhaps a 0mg level.