|Of all of the chemicals in tobacco, nicotine is the one that causes the addiction. It is what keeps you coming back to the cigarette to let the "bad stuff" in and cause so many health problems. Nicotine is not "good" by any means. But we often don't realize that tobacco use is so much more than "just a habit".
When you feel withdrawal symptoms - when you don't have tobacco -- when you get irritable, lose focus and get the jitters - those are all signs of not having the nicotine - a sign of addiction. Most people need help with both addiction to nicotine and the addiction to the behavior before they quit for good.