American Cancer Society answered:
When smokers try to cut back or quit, the lack of nicotine leads to withdrawal symptoms. Withdrawal is both physical and mental. Physically, the body reacts to the absence of nicotine. Mentally, the smoker is faced with giving up a habit, which calls for a major change in behavior. Both the physical and mental factors must be addressed for the quitting process to work.
Those who have smoked regularly for a few weeks or longer, and suddenly stop using tobacco or greatly reduce the amount smoked, will have withdrawal symptoms. Symptoms usually start within a few hours of the last cigarette and peak about 2 to 3 days later when most of the nicotine and its by-products are out of the body. Withdrawal symptoms can last for a few days to up to several weeks. They will get better every day that you stay smoke-free.
Withdrawal symptoms can include any of the following:Dizziness (which may only last 1 to 2 days after quitting)DepressionFeelings of frustration, impatience, and angerAnxietyIrritabilitySleep disturbances, including having trouble falling asleep and staying asleep, and having bad dreams or even nightmaresTrouble concentratingRestlessness or boredomHeadachesTirednessIncreased appetiteWeight gainConstipation and gasCough, dry mouth, sore throat, and nasal dripChest tightness
These symptoms can lead the smoker to start smoking cigarettes again to boost blood levels of nicotine back to a level where there are no symptoms.
Smoking also makes your body get rid of some drugs faster than usual. When you quit smoking, it may change the way your body handles medicines. Ask your doctor if any medicines you take regularly need to be checked or changed after you quit.When smokers try to cut back or quit, the lack of nicotine leads to withdrawal symptoms. Withdrawal is both physical and mental. Physically, the body reacts to the absence of nicotine. Mentally, the smoker is faced with giving up a habit, which... More