Serotonin

• The human brain constantly produces neurotransmitters, which are chemicals that regulate your mood by carrying nerve impulses between nerve cells. There are three neurotransmitters: norepinephrine, dopamine and serotonin. Serotonin helps you maintain a feeling of general well-being and happiness. A serotonin deficiency can lead to a variety of ailments such as insomnia, anxiety and depression. Production of serotonin is stimulated by sunlight and by eating certain foods, and can also be affected by such factors as lifestyle and heredity.
  
  

Nicotine

• A single cigarette contains about 10 mg of nicotine, the chemical within tobacco that makes smoking both pleasurable and addictive. Via inhalation into the lungs, nicotine reaches the brain in eight seconds, immediately stimulating the neurotransmitters. Among the physical sensations a smoker feels are a rapid increase in heart rate and respiration, and increased production of blood glucose. The latter, in fact, may be partially responsible for the increased feelings of alertness most smokers experience after smoking.
  
  

Nicotine and Serotonin

• Although the precise effect that nicotine has on serotonin levels is not entirely clear, nicotine does appear to stimulate serotonin production. According to research at the University of Dundee, smoking appears to cause physical changes in the brain that inhibit serotonin production over a prolonged period. The actual intake of nicotine, however, quickly stimulates serotonin production, but only in the short-term -- as increased serotonin levels only last as long as the cigarette is being smoked. The irony, explained Dundee professor David Balfour, who led the study, is that smokers believe cigarettes provide a sense of calm, when in fact smoking only provides temporary relief from the anxiety caused by smoking in the first place.
  
  

Nicotine Withdrawal and Serotonin

• In 1999, researchers at University of Illinois found that people who try to quit smoking experience some symptoms of depression, which causes them to return to cigarettes for the quick-fix release of serotonin provided by nicotine. In the project, smokers were given a combination of foods that mimicked the reduced levels of serotonin they'll experience when quitting, thus giving them a sample of how they'll feel when they quit. This can help smokers cope with the "distressing thoughts, feelings and moods" they'll experience when they finally quit and don't receive the temporary serotonin lift provided by tobacco, according to Bonnie Spring, University of Chicago.