Immediately after exposure to nicotine, there is a “kick” caused in part by the drug’s stimulation of the adrenal glands and resulting discharge of epinephrine (adrenaline).
This rush of adrenaline stimulates the body and causes an increase in blood pressure, respiration, and heart rate. Like other drugs, nicotine also activates reward pathways in the brain—circuitry that regulates reinforcement and feelings of pleasure.
When tobacco is smoked, nicotine rapidly reaches peak levels in the bloodstream and enters the brain. A typical smoker will take 10 puffs on a cigarette over the roughly 5 minutes that the cigarette is lit. Thus, a person who smokes about 1 pack (20 cigarettes) daily gets 200 "hits" of nicotine to the brain each day.
Among those who do not inhale smoke—such as cigar and pipe smokers and smokeless tobacco users—nicotine is absorbed through mucous membranes in the mouth and reaches peak blood and brain levels more slowly.