I've read the opposite from gwern - that nicotine is safe, and the carcinogens are mostly in the burning of tobacco products. He tested nicotine as a nootropic, apparently has significant effect.
> Nicotine can form carcinogenic Tobacco-specific nitrosamines (TSNAs) through a nitrosation reaction. ... However, nicotine in the mouth and stomach can react to form N-Nitrosonornicotine,[104] a known type 1 carcinogen,[105] suggesting that consumption of non-tobacco forms of nicotine may still play a role in carcinogenesis.