I'm not sure how the stimulant vs. sedative effects work, I'll ask my brother who's a doctor. Plus, there's plenty of gamer smokers at work I can ask about it today! lol
I did read that the acute effects of the cigarette is short-lived, which is why people chainsmoke, etc. which could be reflected in-game by a short buff duration, but a pack contains a lot of uses (compared to say, beer etc), leading to an item that is, in game terms, very easily addictive.
Ooh, there could even be a way of randomizing how many are left in a pack when they're looted alone and not pulled from a carton!