Drugs like Zoloft and Prozac work because they prompt the brain to produce more serotonin: they compensate, in other words, for the deficit of serotonin that some depressed people suffer from. Nicotine appears to do exactly the same thing with the other two key neurotransmitters—dopamine and norepinephrine. Those smokers who are depressed, in short, are essentially using tobacco as a cheap way of treating their own depression, of boosting the level of brain chemicals they need to function normally. This effect is strong enough that when smokers with a history of psychiatric problems give up
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