According to the U.S. Surgeon General, if you're a smoker, stopping smoking is one of the best things you can do for your health. It's one of the best ways to help you live longer and have a better quality of life.      It can be extremely hard to stop smoking though. Author Mark Twain once said, "Quitting smoking is easy. I've done it a thousand times." Perhaps you've tried to quit before and couldn't or maybe you stopped for a while but ended up smoking again. What exactly makes smoking so addictive?      Nicotine is a chemical that is naturally found in the tobacco plant. Believe it or not, it's as addictive as cocaine and heroin. When you have a physical addiction to a drug, you experience very unpleasant withdrawal effects when the drug isn't in your body. It's only human nature to want to avoid discomfort and that's why people that go back to cigarettes.      When you inhale cigarette smoke, nicotine is carried from your lungs to your bloodstream. In fact, nicotine that has been inhaled…