Tobacco contains many toxin chemical substances including nicotine. Nicotine is a highly addictive drug which enters the smoker’s bloodstream through his lungs when the smoker inhales smoke. It is a stimulant that increases the activity in the brain just like coffee. Nicotine works differently for different parts of the brain. When body gets used to nicotine, then it needs certain level in order to function normally otherwise one would feel snappy and edgy.

These are the reasons why so many people find it so hard to quit smoking. Even if they quit, most of them relapse due to nicotine dependency and other social/psychological reasons.