There are many species of tobacco; Nicotiana tabacum (or common tobacco) is used to make cigarettes.
Nicotine, a potent central nervous system stimulant found naturally in the tobacco leaf, is classified as a drug. Nicotine is one of the primary ingredients in tobacco. In higher doses, nicotine is extremely poisonous. It is commonly used as an insecticide.
Tobacco leaves can be burned and inhaled (in the form of cigarettes, cigars, pipes, smoke, etc.) or absorbed through the mouth (in the form of spit tobacco, chew, or snuff). The membranes in the nose, mouth, and lungs act as nicotine delivery systems – transmitting nicotine into the bloodstream and to the brain.
Smokers usually feel dizzy and sick when they first inhale the nicotine in tobacco, but slowly build up tolerance to its effects. Other symptoms new smokers experience includes coughing, a dry, irritated throat as well as nausea, weakness, abdominal cramps, headache, coughing or gagging. These symptoms subside as the user develops a tolerance to nicotine.
Nicotine is extremely addictive. The addictive effect of nicotine is the main reason why tobacco is widely used. Many smokers continue to smoke to be able to avoid the pain of withdrawal symptoms. Smokers also adjust their behavior (inhaling more deeply, for example) to maintain a certain amount of nicotine in the body.
Smokers who usually smoke at least 15 cigarettes each day or smoke their first Cigarette of the day within 30 minutes of waking are most likely to experience nicotine withdrawal symptoms. They will probably find quitting uncomfortable.
Stopping can produce unpleasant withdrawal symptoms such as depression, sleeplessness, irritability, difficulty concentrating, restlessness, anxiety, decreased heart rate, increased appetite, weight gain, and craving for nicotine.
Symptoms peak from 24 to 48 hours after stopping and can last from three days up to four weeks, although the craving for a Cigarette can last for months.
Most smokers make an average of three or four quit attempts before becoming long-term non-smokers. Relapse is the rule rather than the exception and must be seen as part of the process of quitting.