Quote from resinate:
Tobacco/nicotine is a smart drug. Through increasing dopamine and inhibiting MAO enzymes in the brain, it increases concentration, focus and memory and decreases risk and manifestations of cognitive problems such as ADD, Alzheimer's and parkinson's disease. http://en.wikipedia.org/wiki/Nicotine#Therapeutic_uses
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I have read that people with schizophrenia tend to smoke a lot more then people in the general population. I think they said that it somehow helps them as well but I can't recall where I saw the study and I don't feel like looking for it.