INTRODUCTION — Cigarette smoking is the leading preventable cause of mortality, responsible for over seven million deaths worldwide and over 480,000 deaths in the United States annually [1,2]. If current trends continue, tobacco will kill more than eight million people worldwide each year by the year 2030. The three major causes of smoking-related mortality are atherosclerotic cardiovascular disease, cancer, and chronic obstructive pulmonary disease (COPD) .
Those who stop smoking reduce their risk of developing and dying from tobacco-related illnesses [3-5]. Screening all patients for tobacco use and providing patients with behavioral counseling and pharmacotherapy to stop smoking are among the most valuable preventive services that can be offered in health care [6,7].
This topic will discuss the benefits and risks of smoking cessation. Management of smoking cessation, including the use of behavioral and pharmacologic therapies, is discussed in detail separately. (See "Overview of smoking cessation management in adults" and "Behavioral approaches to smoking cessation" and "Pharmacotherapy for smoking cessation in adults".)
BENEFITS OF SMOKING CESSATION — Smoking cessation at any age is associated with substantial health benefits for all people who smoke . The extent of benefit partly depends on the intensity and duration of prior tobacco smoke exposure. Those who stop smoking can be expected to live longer and are less likely to develop tobacco-related diseases, including coronary heart disease, cancer, and pulmonary disease. People also benefit from quitting smoking even after the development of smoking-related diseases, such as coronary heart disease or chronic obstructive pulmonary disease (COPD).
All-cause mortality — Although up to one-half of all people who smoke can be expected to die from a tobacco-related illness , smoking cessation is associated with a mortality benefit for individuals irrespective of age, gender, race, or ethnicity [4,8-10]. Stopping smoking at younger ages, especially before age 40, is associated with a larger decline in premature mortality than stopping at a later age [3,5]. However, quitting smoking after age 60 years is still associated with a lower risk of death compared with older adults who continue to smoke [11-13]. Even in those over age 80, quitting smoking appears to reduce mortality .
Cardiovascular disease — Cigarette smoking is estimated to be responsible for >10 percent of all cardiovascular deaths worldwide  and 33 percent of all cardiovascular deaths in the United States . (See "Cardiovascular risk of smoking and benefits of smoking cessation", section on 'Dose and duration of smoking exposure'.)
Tobacco smoking has multiple harmful effects on cardiovascular pathophysiology, including coronary vasoconstriction, increased hypercoagulability, dyslipidemia, inflammation, and endothelial dysfunction. Smoking cessation reduces biomarkers of inflammation, hypercoagulability, and dyslipidemia.
Smoking cessation is associated with a rapid and substantial reduction in the risk of cardiovascular events (including myocardial infarction, sudden cardiac death, and stroke) for both individuals with and without a prior history of cardiovascular disease . (See "Cardiovascular risk of smoking and benefits of smoking cessation".)
Smoking cessation also reduces the progression of symptomatic peripheral artery disease and is associated with a reduced risk of recurrent stroke (see "Overview of secondary prevention of ischemic stroke"). There is also evidence suggesting that smoking cessation reduces the risk of atrial fibrillation, heart failure, and abdominal aortic aneurysm . (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Smoking cessation'.)
Malignancy — Smoking is a major risk factor for many types of cancers (table 1), and smoking cessation reduces the risk of 12 cancers, including cancers of the lung, larynx, head and neck, esophagus, stomach, colon and rectum, liver, pancreas, kidney, bladder, uterine cervix, and acute myeloid leukemia . The excess cancer risk decreases gradually after an individual stops smoking, dropping to approximately half compared with those who continue to smoke 10 to 15 years after cessation, and continues to decrease thereafter . Among people with a smoking-related cancer, smoking cessation decreases the risk of developing a second smoking-related malignancy and improves the outcomes of cancer treatment [1,8]. Furthermore, the evidence suggests that among cancer patients who are smokers at the time of diagnosis, smoking cessation reduces subsequent all-cause mortality . The relationships between smoking and specific cancers are discussed in detail separately:
●(See "Multiple primary lung cancers".)
Pulmonary disease — Epidemiologic studies indicate that cigarette smoking is the most important risk factor for COPD.
Smoking cessation reduces the accelerated decline of lung function and risk of incident COPD associated with smoking [8,16]. In addition, the majority of people with cough and sputum production with early COPD have an improvement in symptoms in the first 12 months after smoking cessation . The risk of COPD exacerbations also declines over time after smoking cessation . (See "Chronic obstructive pulmonary disease: Risk factors and risk reduction", section on 'Smoking cessation'.)
Smoking is associated with other lung conditions such as combined pulmonary fibrosis and emphysema (CPFE), is causative in the smoking-related interstitial lung diseases [ILDs; desquamative interstitial pneumonia (DIP), respiratory bronchiolitis-associated ILD (RBILD) and pulmonary Langerhans cell histiocytosis (PLCH)], and worsens the symptoms of asthma. Smoking cessation leads to an improvement in respiratory symptoms in these patients. (See "Idiopathic interstitial pneumonias: Classification and pathology", section on 'Smoking-related interstitial pneumonias' and "Pulmonary Langerhans cell histiocytosis", section on 'Role of cigarette smoking' and "Respiratory bronchiolitis-associated interstitial lung disease", section on 'Smoking cessation'.)
Infections — Cigarette smoking is associated with an increased risk of several types of infection, including tuberculosis, pneumococcal pneumonia, meningococcal disease, influenza, and the common cold [19,20]. Although smoking cessation may reduce the risk of several types of infection, there are few data available to support this. (See "Epidemiology of tuberculosis", section on 'Risk factors' and "Microbiology, epidemiology, and pathogenesis of Legionella infection", section on 'Host risk factors' and "Epidemiology of Neisseria meningitidis infection", section on 'Other host factors'.)
Diabetes — The number of cigarettes smoked daily is associated with an increased risk for developing type 2 diabetes mellitus over the long-term. This may be partly due to nicotine’s effect on impaired insulin sensitivity. Although there does appear to be an increased risk of developing type 2 diabetes shortly after quitting tobacco use (perhaps partly due to weight gain), smoking cessation reduces the risk of diabetes after several years of abstinence . (See "Type 2 diabetes mellitus: Prevalence and risk factors", section on 'Smoking'.)
Osteoporosis and hip fracture — Smoking accelerates bone loss and is a risk factor for hip fracture in females . Smoking cessation can reverse loss of bone mineral density and decrease the excess risk of hip fracture after approximately 10 years after quitting tobacco use (relative risk [RR] 0.7, 95% CI 0.5-0.9) [23,24]. (See "Osteoporotic fracture risk assessment", section on 'Cigarette smoking' and "Overview of the management of osteoporosis in postmenopausal women", section on 'Cessation of smoking'.)
Reproductive disorders — Smoking is associated with an increased risk of several reproductive disorders, including complications of pregnancy, premature menopause, erectile dysfunction, and subfertility in both males and females. Maternal smoking during pregnancy is associated with spontaneous abortion, ectopic pregnancy, lower birth weight, and a number of diseases in the fetus, some of which may develop later in life. Maternal smoking cessation results in improved fetal and maternal outcomes . (See "Cigarette and tobacco products in pregnancy: Impact on pregnancy and the neonate" and "Tobacco and nicotine use in pregnancy: Cessation strategies and treatment options".)
Peptic ulcer disease — Gastric and duodenal ulcer disease is more likely to occur and take more time to heal in those who smoke compared with nonsmokers . Smoking is associated with Helicobacter pylori infection, a well-established etiologic agent for peptic ulcer disease . Persistent smoking increases treatment failure rates for H. pylori eradication . Smoking cessation decreases the risk of developing peptic ulcer disease and accelerates the rate of healing in established disease [27,28]. (See "Peptic ulcer disease: Epidemiology, etiology, and pathogenesis".)
Periodontal disease — The number of cigarettes smoked daily is associated with an increased risk of developing periodontal disease, including gingivitis and periodontitis . In a large population-based survey, the risk of periodontitis in those who formerly smoked declined with the number of years after smoking cessation . (See "Overview of gingivitis and periodontitis in adults", section on 'Pathogenesis'.)
Ophthalmologic disorders — Smoking is a risk factor for several ophthalmologic disorders, including the development of cataracts  and age-related macular degeneration [32-34]; smoking cessation appears to decreases these risks over time [35,36]. (See "Cataract in adults", section on 'Risk factors'.)
Postoperative complications — Smoking cessation prior to surgery can prevent postoperative complications, including delayed wound healing and pulmonary complications. Quitting smoking shortly before surgery does not increase postoperative complications, and smoking cessation treatment should be provided to presurgical patients at any time . However, longer periods of smoking cessation prior to surgery are associated with lower rates of postoperative complications. (See "Preoperative medical evaluation of the healthy adult patient", section on 'Smoking' and "Smoking or vaping: Perioperative management", section on 'Perioperative risks of smoking'.)
Other — Smoking has also been associated other adverse health effects. A study using pooled data from five large cohorts including over 420,000 males and 530,000 females aged ≥55 years found that compared with those who never smoked, people who currently smoke had an increased risk of mortality from renal failure (RR 2.0; 95% CI 1.7-2.3), intestinal ischemia (RR 6.0, 95% CI 4.5-8.1), hypertensive heart disease (RR 2.4, 95% CI 1.9-3.0), any infection (RR 2.3, 95% CI 2.0-2.7), breast cancer (RR 1.3, 95% CI 1.2-1.5), and prostate cancer (RR 1.4, 95% CI 1.2-1.7) . The study also found an increased risk of mortality from respiratory illnesses other than pneumonia, influenza, COPD, and pulmonary fibrosis (RR 2.0, 95% CI 1.6-2.4). Smoking cessation decreased these risks, which continued to diminish as the duration of smoking cessation increased.
QUESTIONABLE UTILITY OF SMOKING REDUCTION — Reducing the number of cigarettes smoked daily has been advocated as a possible alternative to complete cessation in patients who are unable to quit smoking. However, few data are available to support a strategy of a reduction in smoking rather than complete cessation. Smoking reduction remains controversial as a strategy for reducing the health risks of those who smoke . Complete smoking cessation is preferable.
Health risks are found even with consistent lower-level smoking (≤10 cigarettes a day). A prospective cohort study of people aged 59 to 82 years at baseline found all-cause mortality and cancer incidence were higher among those who consistently smoked ≤10 cigarettes daily compared with those who never smoked [40,41]. These individuals had higher all-cause mortality (hazard ratio [HR] 1.87, 95% CI 1.64-2.13), and even those who smoked less than one cigarette daily had an elevated risk (HR 1.64, 95% CI 1.07-2.51) . People consistently smoking 1 to 10 cigarettes daily were also 2.34 (95% CI 5 1.86-2.93) times more likely to develop a smoking-related cancer . Quitting smoking lowered their risks; the younger they were when quitting, the lower their risks.
Data are inconsistent as to whether reducing cigarette smoking from higher to lower levels is associated with improved outcomes. At least two prospective cohort studies found that people who reduced smoking by at least 50 percent had no change in all-cause mortality, whereas those who quit smoking completely had decreased risks of all-cause mortality [42,43]. However, another cohort study did find reduced risk for mortality associated with smoking reduction (HR 0.85, 95% CI 0.77-0.95); the benefit with smoking reduction was mainly seen in among those with heavy smoking use and was mainly due to a reduction in cardiovascular mortality . Nevertheless, consistent benefits in cardiovascular disease risk have not been seen with reduction in smoking short of quitting . This is because even low levels of tobacco smoke exposure increase cardiovascular risk. A separate cohort study found that a reduction in smoking may decrease the risk of lung cancer (table 2) . (See "Cigarette smoking and other possible risk factors for lung cancer", section on 'Smoking reduction'.)
One reason that a reduction in smoking may not consistently improve health outcomes is that people may compensate for smoking reduction with increased puffs, volume, or duration in order to maintain nicotine intake and forestall nicotine withdrawal symptoms.
POSSIBLE CONSEQUENCES OF SMOKING CESSATION — Although the potential adverse consequences of smoking cessation are far outweighed by the benefits, these are important to address in order to maximize the likelihood that a patient will successfully quit tobacco use. (See "Behavioral approaches to smoking cessation".)
Nicotine withdrawal syndrome — Nicotine is a potent psychoactive drug that causes physical dependence and tolerance . In the absence of nicotine, an individual develops cravings for cigarettes and symptoms of the nicotine withdrawal syndrome. Symptoms generally peak in the first three days and subside over the next three to four weeks, but cravings for cigarettes may persist for months to years. Nicotine withdrawal symptoms include:
●Increased appetite or weight gain
●Dysphoric, depressed mood, or anhedonia 
●Irritability, frustration, or anger
These factors should be addressed so that people will know what to expect and how to respond if these symptoms occur. Smoking cessation medications, including nicotine replacement therapy, bupropion, and varenicline, relieve the symptoms of nicotine withdrawal (see "Pharmacotherapy for smoking cessation in adults"). Nonpharmacologic approaches can also help to manage nicotine withdrawal symptoms. (See "Behavioral approaches to smoking cessation".)
Weight gain — Weight gain often occurs after cessation of smoking. Weight gain is a concern for some people who are considering smoking cessation. The mechanisms behind weight gain appear to be decreased metabolic rate, increased activity of lipoprotein lipase, changes in food preferences, and increased caloric intake . Weight gain of 1 to 2 kg in the first two weeks is usually followed by an additional 2 to 3 kg weight gain over the next four to five months [50,51]. The average total weight gain is 4 to 5 kg, but may be much greater. Ten percent or more of quitters may gain over 13 kg after smoking cessation. In general, the amount of weight gain is greater in females than males, non-White persons compared with White persons, and those with heavier compared with lighter smoking .
While there are well-recognized health hazards of obesity (see "Overweight and obesity in adults: Health consequences"), these are outweighed by the health benefits of quitting smoking, which are much larger than the additional risk conferred by the weight gain. Behavioral counseling that addresses weight gain, including dietary or physical activity interventions, has some success in limiting weight gain (see "Behavioral approaches to smoking cessation"). Weight gain can also be temporarily blunted in those using bupropion, an antidepressant medication effective for smoking cessation. (See "Pharmacotherapy for smoking cessation in adults", section on 'Bupropion'.)
Psychiatric symptoms — Although nicotine withdrawal syndrome includes symptoms of depression and anxiety, accumulating evidence suggests that smoking cessation does not cause significant adverse psychiatric effects, even in those with psychiatric disorders [53,54]. Overall, such increases in neuropsychiatric symptoms, if any, occur infrequently. Moreover, the benefits of smoking cessation in individuals with and without mental health disorders are substantial and outweigh the possible mental health risks [55,56].
Several studies have found an improvement in anxiety and depression symptoms among persons who quit smoking compared with those who continued to smoke. Individuals with and without a history of mental health disorders experienced an improvement in symptoms.
●A large meta-analysis reported small to moderate improvements in mental health symptoms in individuals who quit smoking compared with those who continued to smoke . These findings were consistent in both unselected populations and subgroups with known psychiatric diagnoses.
●Similarly, a cohort study of 4260 individuals (55 percent of whom reported a history of mental illness) found an association between smoking cessation and a decrease in symptoms of depression and anxiety in both those with and without a history of mental health disorders . In this study, investigators employed multiple methods to control for possible confounding of the relationship between smoking cessation and mental health outcomes.
In contrast, some earlier studies suggested an association between a history of depression and increased neuropsychiatric symptoms during smoking cessation .
Cough and mouth ulcers — A temporary increase in cough and aphthous ulcers can occur in the first few weeks after stopping smoking [58-60]. The pathophysiology is not well-understood. Coughing and aphthous ulcers generally resolve several weeks after the quit date. Individuals with bronchitis who quit may also report an increase in cough, but the most common experience is a decrease is symptoms as noted above .
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Smoking cessation, e-cigarettes, and tobacco control".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Basics topics (see "Patient education: Quitting smoking (The Basics)")
●Beyond the Basics topics (see "Patient education: Quitting smoking (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Cigarette smoking and mortality – Cigarette smoking is the leading preventable cause of mortality and is estimated to cause over seven million deaths worldwide each year. Up to one-half of all those who smoke regularly can be expected to die from a tobacco-related illness. The most important causes of smoking-related mortality are atherosclerotic cardiovascular disease, cancer, and chronic obstructive pulmonary disease (COPD). (See 'Introduction' above.)
●Benefits of smoking cessation – Smoking cessation at any age is associated with substantial health benefits. The extent of benefit partly depends on the intensity and duration of prior tobacco smoke exposure. (See 'Benefits of smoking cessation' above.)
•Smoking cessation is associated with a mortality benefit for individuals of all ages. Stopping smoking before age 40 is associated with a larger decline in premature mortality than stopping at a later age. (See 'All-cause mortality' above.)
•Smoking cessation is associated with a reduced risk of coronary heart disease, cancer, pulmonary disease, infections, and hip fracture. People also benefit from quitting smoking even after the development of smoking-related diseases, such as coronary heart disease or COPD. (See 'Cardiovascular disease' above and 'Malignancy' above and 'Pulmonary disease' above and 'Infections' above and 'Osteoporosis and hip fracture' above.)
●Possible consequences of smoking cessation – Smoking cessation often leads to nicotine withdrawal symptoms, including increased appetite, symptoms of depression or anxiety, insomnia, irritability, difficulty concentrating, and restlessness. Nicotine withdrawal symptoms are temporary and can be treated by pharmacologic or behavioral treatments. (See 'Possible consequences of smoking cessation' above.)
ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Dr. Stephen Rennard, MD, and Mr. David Daughton, MS, who contributed to an earlier version of this topic review.
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