Why is it so hard to quit smoking?

Mark Twain said, "Quitting smoking is easy. I've done it a thousand times." Maybe you've tried to quit too. Why is quitting and staying quit hard for so many people? The answer is nicotine.

Nicotine is a drug found naturally in tobacco. Over time, the body becomes physically and psychologically dependent on nicotine. Studies have shown that smokers must overcome both of these to be successful at quitting and staying quit.

When smoke is inhaled, nicotine is carried deep into the lungs where it is absorbed quickly into the bloodstream and carried to the heart, brain, liver, and spleen. Nicotine affects many parts of the body, including the heart and blood vessels, the hormonal system, the body's metabolism, and the brain. Nicotine can be found in breast milk and in cervix mucous secretions of smokers. During pregnancy, nicotine freely crosses the placenta and has been found in amniotic fluid and the umbilical cord blood of newborn infants. Nicotine is metabolized mainly by the liver and lungs, but a small amount is excreted by the kidneys. Nicotine is broken down by the body into the by-products cotinine and nicotine-N'-oxide.

Several different factors can affect the rate of metabolism and excretion of nicotine. Measurements of nicotine or its by-products will vary depending on the fluid being measured (blood, urine, or saliva). In general, a regular smoker will have nicotine or cotinine present in the body for about 3 to 4 days.

Nicotine produces pleasurable feelings that make the smoker want to smoke more and also acts as a depressant by interfering with the flow of information between nerve cells. As the nervous system adapts to nicotine, smokers tend to increase the number of cigarettes they smoke, and hence the amount of nicotine in their blood. After a while, the smoker develops a tolerance to the drug, which leads to an increase in smoking over time. Eventually, the smoker reaches a certain nicotine level and then smokes to maintain this level of nicotine.