Discover Magazine Looks at Nicotine
Since the debate on the supposed dangers of tobacco has been conveniently shifted to nicotine since e-cigs have removed nearly all other substances of concern, and the quality of the debate from anti-tobacco lobbyists has been scientific dross, on the whole, then it's only fair to present what we actually know about the effects of nicotine on adults, and see if it can be called a 'poison' by themselves in the conventional sense (most everything is poisonous if used incorrectly).
To most adults, the position on a compound depends on risks AND benefits. At this point in time, the data on nicotine neither supports or condemns it. It may be viewed strictly as a poison, but only in the same sense that other phytocompounds like polyphenols (in nuts and berries) may be viewed this way. Some have good and bad effects, but the overall impact is deemed favourable, even though biochemists have viewed them as toxins in the past. We're not saying the balance is in favour of consuming nicotine, but it is clearly the case the data does not justify such extreme negativity about adults taking nicotine at this time. It may increase cancer risk, but it also may protect against brain diseases. So at this point, it's a tough call. And that call would change context entirely if you were more at risk of cancer than brain degeneration, or vice-a-verse. Someone at diagnosed risk of Parkinson's would view the risks very differently, based on what knowledge is available today. Moreover although nicotine is addictive, and that is in itself a bad thing, it isn't particularly strong, comparable to caffeine many scientists are saying. There are other chemical factors in a cigarette that apparently makes it so hard to kick.
Discover Magazine looks into the possible effects of nicotine in this article