" Smokers must recognize that they are drug addicts. Nicotine is a powerfully addictive drug. Once the smoker has smoked for a fairly long time, the body requires maintenance of a certain level of nicotine in the bloodstream. If this level is not maintained, the smoker will experience varying degrees of drug withdrawal. The lower the level, the greater the intensity. As long as any nicotine remains in the bloodstream the body will keep craving its full complement. Once the smoker quits, the nicotine level will eventually drop to zero and all physical withdrawal will cease. Cravings for an occasional cigarette may continue, but this is due to past psychological conditioning and not to a physical dependence.
Cutting down on cigarettes or use of nicotine replacement strategies throws the smoker into a chronic state of drug withdrawal. As soon as the smoker fails to reach the minimum requirement of nicotine, the body starts demanding it. As long as there is any nicotine in the bloodstream, the body will demand its old requirement. Smoking just one or two a day or wearing a patch which is gradually reducing the amount of nicotine being delivered will result in the smoker not achieving the minimum required level, creating a chronic state of peak drug withdrawal.
This state will continue throughout the rest of the smoker's life unless one of two steps is taken to rectify it. First, the smoker can stop delivering nicotine altogether. Nicotine will be metabolized or totally excreted from the body and the withdrawal will stop forever. Or, the smoker can return to the old level of consumptions accomplishing nothing. "
from whyquit.com