Cigarettes contain nicotine, which is highly addictive Nicotine alters the balance of 2 chemicals called dopamine and noradrenaline in your brain.When nicotine changes the levels of these chemicals, your mood and concentration levels change. Many smokers find this enjoyable.The changes happen very quickly. When you inhale the nicotine, it immediately rushes to your brain, where it produces feelings of pleasure and reduces stress and anxiety. This is why many smokers enjoy the nicotine rush and become dependent on it. The more you smoke, the more your brain becomes used to the nicotine.This means you have to smoke more to get the same effect. Nicotine is the chemical in tobacco that makes it hard to quit. Nicotine produces pleasing effects in your brain, but these effects are temporary.