Tobacco contains nicotine which affects the nervous system as both a stimulant and a depressant. Tobacco contains many other substances known as tar which are harmful to the body. Breaking a tobacco habit is just as hard as breaking the habit of cocaine or alcohol because of the effects of nicotine. People experience withdrawal symptoms when they try to quit smoking.Nicotine elevates the sense of well-being and stimulates memory and how alert a person feels. It causes blood sugar level to increase resulting in more energy. It also speeds up metabolism resulting in weight gain, when someone tries to quit smoking.There are many negative aspects to nicotine addiction including risk of cancer, heart attack and stroke. But, it is the supposed positive effects that cause the habit to become so difficult to break.