[chris11]

That is a good point. When addicts use drugs their stress is reduced. But nicotine is unique in that its profile depends on the dose.

When smokers want to have more concentration, they take short and quick puffs. This gets a low level of nicotine in the blood. At a low dose, nicotine increases norepinephrine and dopamine. So it acts like a stimulant.

When smokers want to relax, they take long and deep puffs. This increases the dose of nicotine. And at high doses, it affects serotonin and opiate levels in the brain and acts like a sedative.

http://en.wikipedia.org/wiki/Nicotine#Psychoactive_effects