MSD Manual

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Judith J. Prochaska

, MD, Department of Medicine, Stanford University

Last full review/revision Aug 2018| Content last modified Aug 2018
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Tobacco use is a major individual and public health problem. Dependence develops rapidly. Major consequences include premature death and morbidity caused by cardiovascular disease, lung and many other types of cancer, COPD, and other disorders. All patients who smoke should be offered smoking cessation interventions.

The prevalence of tobacco use in the US has declined over the past 50 years, but because of population growth, the number of smokers has remained relatively stable at nearly 40 million.

Tobacco is used because of the effects of its main active ingredient: nicotine. Nicotine is highly addictive when inhaled into the lung. The combustion products of tobacco contain other substances that can cause significant morbidity and mortality.


Tobacco is often smoked, primarily in the form of cigarettes. Cigarette smoking is the most harmful form of tobacco use. However, all tobacco products contain carcinogens and other toxins; smokeless tobacco products are not safe alternatives to smoking.


The percentage of people in the US who smoke cigarettes has declined since 1964, when the Surgeon General first publicized the link between smoking and ill health. Nevertheless, about 15% of adults in the US still smoke.

Smoking is more prevalent among the following groups:

  • Men

  • Young adults

  • People who identify as lesbian, gay, bisexual, or transgender

  • Those who are disabled

  • People with less than a high school education

  • People living at or below the poverty income level

  • People with psychiatric disorders (including alcohol and substance use)

  • American Indian and Alaskan Native people

Smoking is less common among Hispanics and least common among Asian American women.

Nearly all smokers start before the age of 18, making tobacco use a pediatric disorder. Each day, over 3000 youth under age 18 smoke their first cigarette and over 2000 youth and young adults who have been occasional smokers become daily cigarette smokers. Major risk factors for childhood initiation of smoking include smoking among family members and peers as well as exposure to tobacco advertising and marketing in print, online, and at the point of sale in stores, along with tobacco use scenes in movies and video games.

Other tobacco and nicotine products

Cigar and pipe smoking are less common in the US. In 2015, an estimated 12.5 million people aged 12 or older (4.7% of that population) were cigar smokers and 2.3 million (0.8%) were pipe smokers. These percentages have remained relatively stable over the past 15 years. Health harms of pipe and cigar smoking include cardiovascular disease; COPD; cancers of the oral cavity, lung, larynx, esophagus, colon, and pancreas; and periodontal disease and tooth loss.

E-cigarettes or vape pens are devices consisting of a battery and a cartridge containing an atomizer to heat a solution with propylene glycol, glycerol, and usually but not always nicotine. While there is no combustion involved in using e-cigarettes, the aerosol emitted from the device is more than water vapor. In addition to often containing nicotine, e-cigarette aerosol has ultrafine particles, which can be inhaled deeply into the lungs; flavoring such as diacetyl, a chemical linked to serious lung disease; volatile organic compounds; cancer-causing chemicals; and heavy metals (eg, nickel, tin, and lead), though all at lower levels than in combusted tobacco smoke. While the long-term effects of inhaling e-cigarette aerosol are not clearly known, it is reasonable to speculate that they are likely to be less detrimental than the well-known adverse effects of smoking combustible cigarettes. For people who use e-cigarettes and continue to smoke, a common practice of dual users, the health benefits of e-cigarette use are unproven. The effects of maternal e-cigarette use on fetal development are unknown. as are the effects of e-cigarette use on the developing adolescent brain. E-cigarette use among high school students now exceeds combustible tobacco use (11.3% use e-cigarettes vs 8.0% who smoke combustible cigarettes), according to the Centers for Disease Control and Prevention (CDC). The long-term risks of e-cigarette smoking, a relatively new phenomenon, are unknown.

Smokeless tobacco (chewing tobacco and snuff) is used by about 2.5% of people 18 yr and about 5.8% of high school students. Toxicity of smokeless tobacco varies by brand. Harms include cardiovascular disease, oral disorders (eg, cancers, gum recession, gingivitis, periodontitis and its consequences), and teratogenicity.

Inadvertent oral exposure to tobacco is uncommon but may cause serious toxicity. Young children occasionally ingest cigarettes from unguarded packs, cigarette butts from ashtrays, e-cigarette liquid, or nicotine gum. In 2014, 13,702 cases of potentially toxic exposure to tobacco and nicotine products were reported to the American Association of Poison Control Centers (AAPCC), with > 75% occurring in children < 6 yr; the most common source was cigarettes and the most commonly affected age group was < 1 yr.

Cutaneous exposure to tobacco can be toxic. Tobacco harvesters and processors who handle raw tobacco (especially if wet) without protection may absorb nicotine through the skin and develop symptoms of nicotine toxicity, a syndrome termed green tobacco sickness.

Passive exposure to tobacco smoke (second-hand smoke) occurs when people inhale smoke from a nearby smoker. The amount inhaled (and thus its effects) varies with the proximity and duration of exposure as well as the environment (eg, closed space) and ventilation.


Nicotine is a highly addictive drug present in tobacco and is a major component of cigarette smoke. Cravings can begin within days of first use. Nicotine stimulates brain nicotinic cholinergic receptors, releasing dopamine and other neurotransmitters, which activate the brain reward system during pleasurable activities in a manner similar to that of many other addictive drugs (see Overview of Substance-Related Disorders). Dopamine, glutamate, and gamma-aminobutyric acid (GABA) are important mediators of nicotine dependence.

Psychologic dependence exists when people smoke to affect their mood or avoid withdrawal symptoms; it can develop within 2 wk after starting smoking and occurs in up to about 25% of adolescents who try smoking. Physical dependence (ie, occurrence of withdrawal symptoms with cessation) also develops within 2 wk. People smoke to feed their nicotine dependence but simultaneously inhale thousands of other components, including carcinogens, noxious gases, and chemical additives that are a part of cigarette smoke. These toxic components, rather than nicotine, are responsible for the multiple health consequences of smoking. The tar byproducts from tobacco smoke induce metabolizing enzymes in the liver (primarily CYP2A6), leading to multiple potential drug interactions.

Chronic effects of smoking

Smoking harms nearly every organ in the body. Smoking is the leading cause of preventable mortality in the US, accounting for an estimated 520,000 deaths/yr, or about 20% of all deaths. About two in three long-term smokers die prematurely of a disease directly caused by smoking, losing 10 to 14 yr of life (7 min/cigarette) on average.

The major chronic effects are an increased likelihood of the following:

Coronary artery disease accounts for about 30 to 40% of all tobacco-related deaths. Risk of MI is increased by > 200% if smoking < 1 pack/day and risk of cardiovascular mortality is increased by > 50% over a 35-yr period. Mechanisms include endothelial cell damage, transient increases in BP and heart rate, induction of a prothrombotic state, and adverse effects on serum lipids.

Lung cancer accounts for about 15 to 20% of tobacco-related deaths. Smoking tobacco is the most common cause of lung cancer in North America and Europe, and accounts for more than 87% of lung cancer deaths. Inhaled carcinogens are directly exposed to lung tissue.

COPD accounts for roughly 20% of tobacco-related deaths. Tobacco is the most common cause of COPD and accounts for 61% of all pulmonary disease deaths. Smoking impairs local respiratory tract defense mechanisms and, particularly in genetically susceptible people, tends to accelerate decline in pulmonary functions. Coughing and dyspnea on exertion are common.

Less common yet serious smoking-related disorders include age-related macular degeneration, noncardiac vascular diseases (eg, stroke, aortic aneurysm), other cancers (eg, bladder, cervical, colorectal, esophageal, kidney, laryngeal, liver, oropharyngeal, pancreatic, stomach, throat, acute myeloid leukemia), diabetes, pneumonia, rheumatoid arthritis, and tuberculosis.

In addition, smoking is a risk factor for other conditions that convey significant morbidity and disability, such as frequent URIs, asthma, cataracts, infertility, erectile dysfunction, premature menopause, peptic ulcer disease, osteoporosis, hip fractures, and periodontitis.

Secondhand smoke

Secondhand smoke is tobacco smoke that is exhaled by a smoker or given off from the end of a lit cigarette. Secondhand smoke is linked to the same neoplastic, respiratory, and cardiovascular diseases that threaten active smokers. The risk of illness is related to dose. For example, between spouses, average risk is increased by about 20% for lung cancer and by about 20 to 30% for coronary artery disease.

Children exposed to cigarette smoke lose more school days because of illness than nonexposed children. Treating children for smoking-related illnesses is estimated to cost $4.6 billion/yr.

Overall, secondhand smoke is estimated to cause 50,000 to 60,000 deaths each year in the US (between 2% and 3% of all deaths), with lost productivity costs due to premature deaths from secondhand smoke exposure estimated to be $5.6 billion per year. These findings have led states and municipalities across the US to ban smoking within workplaces in an effort to protect the health of workers and others from the substantive risks of environmental tobacco smoke. In 2000, no state or the District of Columbia had a comprehensive indoor smoke-free ordinance in effect, this increased to 26 by the end of 2010, and one additional state was added by the end of 2015. In some states without statewide comprehensive smoke-free laws, substantial progress has been made at the local level in adopting comprehensive smoke-free laws. However, 8 states without statewide comprehensive smoke-free laws (Connecticut, Florida, New Hampshire, North Carolina, Oklahoma, Pennsylvania, Tennessee, and Virginia) have preemption statutes that prohibit adoption of local smoke-free laws.

Smoking during pregnancy increases the risk of spontaneous abortion, ectopic pregnancy, preterm birth, and congenital defects (see Social and Illicit Drugs During Pregnancy). Infants born of mothers who smoke tend to have a lower birth weight and are at increased risk of

Indirect effects of smoking

Indirect effects of smoking can be serious.

Smoking-related fires occur in about 7600 residential buildings in the US each year, according to the Federal Emergency Management Agency (FEMA). These fires cause about 365 deaths, 925 injuries, and $326 million in property loss annually. Such fires are the leading cause of deaths resulting from unintentional fires in the US.

Drug interactions with smoking are common. The effects are largely due to induction of metabolic enzymes in the liver by tar byproducts of smoking. Nicotine does not similarly induce metabolic enzymes, and thus drug-induction effects do not occur with nicotine replacement therapy or e-cigarettes. Levels and sometimes clinical effects of the following drugs are decreased by chronic smoking, primarily by induction of CYP2A6 enzymes:

  • Antiarrhythmics (some): Flecainide, lidocaine, mexiletine

  • Antidepressants (some): Clomipramine, fluvoxamine, imipramine, trazodone

  • Antipsychotics (some): Chlorpromazine, clozapine, fluphenazine, haloperidol, olanzapine, thiothixene

  • Caffeine

  • Estrogens (oral)

  • Insulin (delayed absorption caused by skin vasoconstriction)

  • Pentazocine

  • Theophylline

Two exceptions are benzodiazepines, for which drug sedation effects are decreased likely due to the stimulating effects of nicotine, and beta-blockers, with reduced BP and heart rate control possibly caused by nicotine-mediated sympathetic activation.

Symptoms and Signs

Acute effects

Nicotine slightly increases heart rate, BP, and respiratory rate. Smokers may feel increased energy and arousal, increased ability to concentrate, decreased tension and anxiety, and a sense of pleasure and reward. Nausea is common on a person's first exposure to nicotine. Nicotine reduces appetite and can be a behavioral substitute for eating.

With combustible tobacco, exercise tolerance tends to decrease because of respiratory tract irritation. Low-grade carbon monoxide toxicity can also limit exercise tolerance, but this is probably only a factor in elite athletes.

Toxicity or overdose

Acute nicotine poisoning is usually caused by oral (eg, children eating a cigarette or nicotine gum or ingesting e-liquid) or dermal (eg, handling raw tobacco products) exposure, rather than smoking.

Mild nicotine toxicity, as is common with green tobacco sickness and minor ingestions by children (eg, < 1 cigarette or 3 butts), typically manifests with nausea, vomiting, headache, and weakness. Symptoms spontaneously resolve, usually in 1 to 2 h after ingestion if poisoning is mild; however, symptoms can persist for 24 h if poisoning is severe.

Severe nicotine poisoning causes a cholinergic toxidrome with nausea, vomiting, salivation, lacrimation, diarrhea, urination, fasciculations, and muscle weakness. Patients usually have crampy abdominal pain and, if poisoning is very severe, arrhythmias, hypotension, seizures, and coma. The fatal dose of nicotine is about 60 mg in adult nonsmokers, 120 mg in adult smokers, and as little as 10 mg in young children. Each cigarette contains about 8 mg of nicotine (only about 1 mg is absorbed by smoking). However, the amount ingested by children is usually difficult to ascertain by history because ingestion is rarely observed; any ingestion should be considered potentially dangerous.

Chronic effects

Findings due to smoking itself include yellow stains of teeth and fingers, and in comparison to age-matched controls, weight is slightly lower (≤ 5 kg difference), skin is drier and more wrinkled, and hair is thinner.

Other symptoms are those of smoking-related lung and cardiovascular disease. Chronic cough and dyspnea on exertion are common. Circulatory and respiratory impairments decrease exercise tolerance, often resulting in a more sedentary lifestyle and thus further lowering of exercise tolerance.


Smoking cessation often causes intense nicotine withdrawal symptoms, primarily a craving for cigarettes but also other symptoms (eg, anxiety, difficulty concentrating, sleep disruption, depression) and eventual weight gain.


  • Direct questioning

Acute toxicity is not always apparent on history. Children may not have been observed ingesting tobacco, nicotine gum or e-liquids, and patients with green tobacco sickness may not think to mention that they handle tobacco. Thus, children and agricultural workers presenting with typical symptoms, particularly cholinergic manifestations, should be queried about possible tobacco exposure. Testing is not necessary.

Of the > 70% of smokers who present in a primary care setting every year, only a minority receive counseling and drugs to help them quit. To maximize identification of smokers and thus the public health benefit of smoking cessation, all patients should be asked about tobacco use during medical visits regardless of presenting symptoms and particularly during visits for symptoms possibly related to smoking (eg, circulatory or respiratory symptoms). In addition, assessing patients' quantity of use (the number of cigarettes smoked per day) and how soon they smoke upon wakening (within 30 minutes is a sign of problematic use) can help indicate the severity of tobacco dependence and nicotine addiction and help guide selection and dosing of cessation drugs.


Preventing youth smoking is important because 90% of smokers start before the age of 18, and very few adults will begin to smoke or use smokeless tobacco products after age 26. An estimated 5.6 million youth <18 in the US today will die prematurely from a smoking-related illness; these deaths can be averted through concerted public health measures and regulatory actions. For example, restricting depictions of smoking in movies and video games, raising the minimum age of smoking to 21, banning menthol and characterizing flavors in all forms of tobacco, increasing the price of cigarettes, and restricting tobacco industry product discounting at the point of sale are important interventions for preventing smoking among youth. The National Academies of Sciences has concluded that there is substantial evidence that e-cigarette use increases the risk of ever using combustible tobacco cigarettes among youth and young adults. Still unknown is whether this translates into sustained use of combusted cigarettes.


Skin exposed to nicotine should be irrigated. Otherwise, treatment for acute nicotine poisoning is supportive. Gastric emptying is not recommended. In patients with mild symptoms or who have vomited, charcoal is not given; some clinicians would recommend charcoal for patients who have severe symptoms or have ingested large quantities and have not vomited. Airway protection and assisted ventilation may be needed for patients who are obtunded, have excessive respiratory secretions, or have respiratory muscle weakness. Seizures are treated with benzodiazepines. Shock is treated with IV fluids and, if fluids are ineffective, pressors. Atropine can be considered for patients who have excessive respiratory secretions or bradycardia; otherwise, anticholinergics are not recommended.

All smokers should be advised to stop smoking by their health care provider. Assistance with quitting includes smoking cessation counseling and typically drug treatment (see table Drugs for Smoking Cessation. Referrals to the tobacco quit-line (1-800-QUIT-NOW), web sites (eg,, and other resources may help. Pregnant women who smoke should be advised to stop smoking and helped to quit by intensive smoking cessation counseling. However, the 2017 US Preventive Services Task Force concluded that the evidence was insufficient to assess the benefits and harms of drug therapy for tobacco cessation in pregnant women (see Tobacco Smoking Cessation in Adults, Including Pregnant Women: Behavioral and Pharmacotherapy Interventions).

Key Points

  • Cigarette smoking is the leading cause of preventable mortality in the US.

  • Most smokers start before age 18.

  • Cravings can begin within days of first use and persist long after quitting smoking.

  • Cigarettes create and sustain addiction through the rapid delivery of nicotine to the brain.

  • In addition to nicotine, cigarette smoke contains carcinogens, noxious gases, and chemical additives, which are responsible for the adverse health effects that cigarettes cause.

  • Harmful effects of smoking include increased risk of debilitating and fatal disorders (eg, lung cancer, COPD, coronary artery disease), residential and wild fires, and drug interactions.

  • Nicotine acts as a mild stimulant acutely in the usual doses but can cause a cholinergic toxidrome in acute overdose (usually due to oral ingestion or direct dermal exposure).

  • Ask all patients about smoking, regardless of presenting symptom; advise all smokers to quit; offer assistance to support quitting; and arrange follow-up to prevent relapse.

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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