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Judith J. Prochaska

, PhD, MPH, Department of Medicine, Stanford University

Last full review/revision Dec 2020| Content last modified Dec 2020

Smoking tobacco is harmful to almost every organ in the body.

  • Smoking increases the risk of heart attack, lung cancer, chronic obstructive pulmonary disease (COPD), and other disorders.
  • Nicotine is the addictive substance present in tobacco.
  • People who stop using nicotine may become irritable, anxious, sad, and restless during the period of withdrawal.

(See also Smoking Cessation and Vaping.)

Nicotine is the substance in tobacco (present in cigarettes, cigars, and pipe and chewing tobacco as well as e-cigarettes) that users become dependent on. In addition to nicotine, smoked cigarettes contain tar and carbon monoxide, along with almost 4,000 other ingredients, many of which are toxic. Nicotine is also the active ingredient in some drug products used to help people quit smoking. When delivered by smoking cigarettes, nicotine reaches the brain rapidly (within 10 seconds), and is thus highly addictive. In contrast, delivery of nicotine by a transdermal patch is slow and steady and does not cause addiction.

Most nicotine exposure is from smoking tobacco, although children may accidentally eat it (usually cigarettes or butts left in ashtrays or sometimes nicotine gum, patches, or e-liquid), and some people use smokeless tobacco. Nearly all smokers smoke cigarettes. A small percentage of smokers smoke cigars or pipes.

Cigarette smoking remains the leading cause of preventable disease and death in the United States and globally. About two in three long-term smokers will die prematurely of a disorder caused by smoking. Over half a million Americans die each year from a tobacco-related disease: that is, 1 in 5 U.S. deaths are related to smoking. Smoking is deadly because smokers inhale hundreds of substances, many of which can cause cancer, heart disease, and lung disease. Smokeless tobacco products are not safe alternatives to smoking because they too contain toxins.

Smoking also presents another danger in that it is the most common cause of unintentional home fires in the United States. The Federal Emergency Management Agency (FEMA) estimates that about 7,600 smoking-related fires occur in residential buildings each year, causing about 365 deaths, 925 injuries, and $326 million in property loss.

Currently, about 14% of U.S. adults smoke cigarettes, compared to the mid-1960s when 1 in 2 men and 1 in 3 women were smokers. Yet, due to population growth, the absolute number of smokers in the United States has remained about the same at nearly 35 million adults. Cigarettes are marketed heavily, to adolescents as well as adults, primarily at the point of sale. Every day, about 1,600 youth under age 18 smoke their first cigarette, and nearly 200 youth become daily cigarette smokers.

Pregnant women and children

Smoking during pregnancy robs the developing fetus of oxygen and can cause low birth weight, preterm birth, and fetal death. Smoking during pregnancy also increases risk of sudden infant death syndrome (SIDS). Smoking is a pediatric disease: 9 in 10 smokers start before the age of 18, which is prime time for brain development.


Smoking is harmful to almost every organ in the body.

Immediate effects

Nicotine is a stimulant that activates the pleasure center in the brain. When obtained through smoking, nicotine can increase energy and concentration and decrease appetite. Once a person is addicted, smoking will reduce symptoms of nicotine withdrawal and may feel relaxing. People not used to nicotine may have nausea, flushing, or both.

People who handle large amounts of tobacco leaves may absorb nicotine through their skin and develop nausea, vomiting, diarrhea, sweating, and weakness. This illness has been termed green tobacco sickness.

Children who eat tobacco products or nicotine gum or ingest e-liquid can develop nausea, vomiting, diarrhea, sweating, and weakness, along with agitation and confusion, sometimes from as little as one cigarette. However, serious or fatal toxicity in children is uncommon, in part because the vomiting empties the stomach.

Long-term effects

The leading smoking-related health problems are the following:

Smoking also increases the risk of stroke, other cancers (such as bladder, cervical, colorectal, esophageal, kidney, liver, pancreatic, throat, and stomach), pneumonia and other respiratory infections, asthma, osteoporosis, periodontitis (gum disease), peptic ulcer disease, cataracts, erectile dysfunction, and fertility problems.

Secondhand smoke

People who do not smoke but who are exposed to smoke from a burning cigarette or the smoke exhaled by a nearby smoker (passive, or secondhand smoking) can develop many of the same disorders as smokers, particularly with repeated and sustained exposure. The Surgeon General concluded there is no safe level of secondhand smoke exposure.

Children exposed to cigarette smoke lose more school days because of illness than nonexposed children.

Smokeless tobacco

The toxicity of smokeless tobacco can vary from one brand to another. Risks include heart and blood vessel disorders, mouth disorders (for example, cancers, gum recession, gingivitis, and periodontal disease and its consequences), and tumors.


E-cigarettes or vape pens are devices consisting of a battery and a cartridge containing an atomizer to heat a solution, often with nicotine. Long-term risks of e-cigarettes are unknown.

Other effects

Smoking can interact with other drugs. The effects are largely due to tars in the liver as a by-product of smoking and not due to the nicotine; hence, most effects are not seen with nicotine replacement therapy (NRT). Smoking dries and wrinkles a person's skin, thins the hair, and turns the teeth and fingers yellow. Smokers tend to weigh about 10 pounds less than they would if they did not smoke, but not everyone gains weight when they quit smoking. Also, the harmful effects of smoking far outweigh the risks of weight gain. Employees who smoke cost employers on average over $5,000 more per year than nonsmoking employees due to greater health care costs and more missed days of work. Smoking increases the risk of unemployment and makes it harder to find re-employment.

Withdrawal symptoms

Nicotine withdrawal may result in many unpleasant symptoms, including a craving for nicotine, irritability, anxiety, poor concentration, restlessness, trembling (tremor), depressed mood, weight gain, headaches, drowsiness, and stomach upset. Withdrawal is most troublesome in severely dependent people. The symptoms of nicotine withdrawal peak in the first 3 days and subside over 2 to 4 weeks, but some symptoms, such as craving, may continue longer.


  • Interview of smoker

It is recommended that doctors ask everyone about tobacco use. For many people, smoking is an addiction needing medical treatment. Assessing a person's quantity of use (the number of cigarettes smoked per day [presently and in the past]) and how soon they smoke upon wakening (within 30 minutes is a useful measure) can provide an indication of the severity of tobacco dependence and nicotine addiction. Responses also can help guide the choice of cessation medication and its dosing.

Nicotine poisoning can be overlooked. For example, children may swallow cigarettes or nicotine gum without being seen. Even when children are observed with tobacco in their mouth, it can be difficult to tell how much they have actually swallowed. People with green tobacco sickness may not connect their symptoms with handling tobacco.


  • Treatment of symptoms
  • Quitting smoking

Emergency treatment is rarely required except for children who have eaten products that contain nicotine. Doctors usually give activated charcoal by mouth to absorb any drug remaining in the gastrointestinal tract. Children who are very agitated may be given a sedative such as lorazepam.

Stopping smoking can be very difficult and relapse is common. Quitting successfully usually requires many attempts. Evidence-based treatments more than double the chances of long-term success.

More Information about Smoking

The following English-language resources may be useful. Please note that The Manual is not responsible for the content of these resources.

    • American Cancer Society: Stay Away from Tobacco: Information about the risks of using tobacco products and resources on how to quit
    • American Lung Association: Stop Smoking: Tools, tips, and support for smokers or their loved ones to help end addiction to tobacco
    • Cancer.Net: Stopping Tobacco Use After a Cancer Diagnosis: Resources to help quit tobacco use after receiving a cancer diagnosis
    • Centers for Disease Control and Prevention: Tips from Former Smokers: Stories from people living with smoking-related disease and resources for tobacco users and public leaders to help people quit smoking
    • Centers for Disease Control and Prevention: Youth Tobacco Prevention: Fact sheets, infographics, and other resources for teachers, coaches, parents, and others involved in anti-smoking, youth education
    • The National Cancer Institute (NCI) resource to help reduce smoking rates in the US, particularly among certain populations, by providing cessation information, a tailored quit plan, and text-based support

Drugs Mentioned In This Article

Generic Name Select Brand Names
lorazepam ATIVAN

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