What happens when smokers abruptly stop using nicotine? While you're using nicotine-containing products, your body adapts the way it works to compensate for the effects of the nicotine. For example, neurons in your brain might increase or decrease the number of receptors or the amount of different neurotransmitters affected by the presence of nicotine. When you no longer have nicotine in your body, these physiological adaptations for nicotine remain. The net result is that your body can't function the same way in the absence of the drug as it did before, at least in the short term. People trying to quit nicotine experience this as:
Irritability
Anxiety
Depression
Craving for nicotine
Over a period of about a month, these symptoms and the physiological changes subside. But for many smokers, even a day without nicotine is excruciating. Every year, millions of people try to break the nicotine habit; only 10 percent of them succeed. Most people throw in the towel after less than a week of trying,
For more info go to
Howstuffworks "How Nicotine Works"