Actually I think it's because there are other substances in cigarettes than just nicotine that have a somewhat psychoactive effect. People mention MAOIs a lot, but I'm finding that adding WTA to my regular ejuice has a TREMENDOUS effect on my state of mind/mood.
You may have seen some mention around here of the "3 days/3 wks/3 mos" trouble spots. When I first quit, back in February, after a few weeks I was so negative, so depressed, and utterly convinced that everyone here hated me and wished I would just leave. Then I realized I was right at 3 weeks smoke-free! Within a week, the negative feelings had passed, but when I got close to 3 months smoke-free, I had the same thing all over again, plus I felt very angry. And again, the negative feelings faded within a week.
When I quit this time, I already planned to add some WTA when I got close to 3 wks, but I started having some serious cravings in the middle of my 2nd week, so I went ahead and added the WTA then -- the cravings completely disappeared, AND I sailed right thru the 3 wk mark without ANY of those depressed feelings.
I've struggled with depression and anxiety my whole life, and now I understand that this sabotaged all my efforts to quit smoking, before e-cigs; I was self-medicating, and when the medication was taken away, my life became unlivable. Nicotine replacement can help a great deal with this type of problem, but it's not the whole story, since there is more than one chemical in cigarettes which is greatly beneficial for people with depression an/or anxiety -- it's the whole tobacco-alkaloid cocktail.
I'm not saying that WTA will definitely make your depression go away; what I am saying is that for people with these kinds of problems, WTA may be more beneficial than nicotine alone, in quitting cigarettes. I don't know if that means I'll always need WTA; I guess I'll find out. I do know that I won't be discontinuing the WTA until some time after the 3 month mark, and then, I'll do it slowly rather than all at once, and maybe that way, I can keep my mood disorders from sabotaging my efforts at staying free of cigarettes.
Andria