Small amounts of many things are like that.
In the central nervous system
Effect of nicotine on dopaminergic neurons
By binding to nicotinic acetylcholine receptors, nicotine increases the levels of several neurotransmitters - acting as a sort of "volume control". It is thought that increased levels of dopamine in the reward circuits of the brain are responsible for the euphoria and relaxation and eventual addiction caused by nicotine consumption. Nicotine has a higher affinity for acetylcholine receptors in the brain than those in skeletal muscle, though at toxic doses it can induce contractions and respiratory paralysis.[20] Nicotine's selectivity is thought to be due to a particular amino acid difference on these receptor subtypes.[21]
But many other chemicals are like that - some benefits (sometimes important benefits) in small amounts while toxic in larger amounts, too. http://www.actionbio...nt/trautmann.html
Cigarettes are bad. Cigarettes are primarily a nicotine delivery device because nicotine is addictive (thus cigarettes are very profitable for the manufacturers). Nicotine is too strong a poison to play up its benefits "absent the other chemistry from a cigarette" - it's not delivered that way.
But one can easily argue that tobacco built America, so it's not totally black and white...
My $0.02.
Cheers,
Scott.
