What makes people addicted is nicotine, which can cause addiction or dependence. Nicotine spreads throughout the body through the mucous membranes of the lungs and mouth, and after entering the brain, nicotine mimics the action of acetylcholine, a central neurotransmitter that binds to nicotine receptors on the surface of many neurons.

Nicotine has a stimulatory effect on the central nervous system, particularly in the "reward circuit". It releases more dopamine by activating the nerves involved.

Tobacco use is a risk factor for six of the world's top eight causes of death. Tobacco use can cause tumors of the lungs, larynx, kidneys, bladder, stomach, colon, mouth, and esophagus, as well as leukemia, chronic bronchitis, chronic obstructive pulmonary disease, ischemic heart disease, strokes, miscarriages, preterm births, birth defects, infertility, and other diseases.

It causes great but preventable suffering and serious productivity losses. In addition, tobacco use has significant economic costs for families and countries, including lost income, decreased productivity, and higher health care costs.

Baidu Encyclopedia - Cigarettes