Nicotine is one of the main ingredients in tobacco. Nicotine is a powerful drug that speeds up the brain and central nervous system. It triggers the release of a chemical in your brain (dopamine) that boosts your mood, makes you feel calm, and at the same time, can make you feel more alert. The nicotine in cigarette smoke is absorbed through the skin lining of the mouth and the nose. The nicotine level in your blood peaks within 10 seconds of inhaling (breathing in) cigarette smoke into your lungs.
Over time, your brain adjusts to the stimulation ("buzz") from nicotine and lowers your natural energy level or mood. You may then start to crave a cigarette for a boost. The more you smoke the more nicotine you need to feel good. Soon, your body craves nicotine to feel "normal." Being without nicotine for even a few hours can cause withdrawal symptoms like headaches, depression, anger, anxiety, and problems sleeping.
Cigarettes have a chemical in them called nicotine, this makes the body addicted to things. Not a mental addicting like you get with a video game, but a physical addiction. This is why it's so hard for some people to quit, their body actually craves the cigarettes.
Smoking cigarettes is highly addictive. Along with the physically addictive nicotine in cigarettes, the act of smoking is very psychologically addictive. It's an extremely difficult addiction/habit to break, so if you don't smoke now -- do NOT start!! If you do smoke, try to quit... :)
Nicotine is a drug. It has nothing to do with "feeling good" or "not feeling good" as the other member posted. You can smoke too much and develop a "nicotine headache" just as you would if you abruptly stopped intake of caffeine if you are a big soda or coffee drinker. A person becomes addicted to the nicotine. It is the hardest "drug" to kick so to speak. Stronger than cocaine, heroin, etc. Many people who never smoked have died from lung cancer. You become physically addicted first, then it becomes a mental addiction as well, i.e., having to have a cigarette with your morning coffee, talking on the phone, after eating, etc. The tobacco has nothing to do with it. All nicotine.