Nicotine

A drug in tobacco which acts as a stimulant and is responsible for dependence on tobacco. After inhalation, the nicotine in tobacco smoke passes rapidly into the bloodstream. The drug acts on the nervous system until broken down by the liver and excreted in the urine. Nicotine acts primarily on the autonomic nervous system, which controls involuntary body activities such as the heart rate. In habitual smokers, the drug increases the heart rate and narrows the blood vessels, the combined effect of which is to raise blood pressure. Nicotine also stimulates the central nervous system, thereby reducing fatigue, increasing alertness, and improving concentration. Stopping smoking often causes withdrawal symptoms such as headaches and difficulty in concentrating. Nicotine replacement therapy, such as the use of nicotine skin patches and chewing gum, can be effective in aiding withdrawal from nicotine. (See also smoking.)