Irritable Bowel Syndrome


In irritable bowel syndrome (IBS), the bowel appears normal but does not function correctly; yet, the reason for this is unknown. IBS is also called spastic colon, mucous colitis, and irritable colon.


Between 10% and 15% of the world's population— more than 70 million people—are thought to be affected by IBS. Because of this high percentage, IBS is considered one of the most common medical disorders. The disorder appears to be most common in Western countries; however, poor access to medical care, different cultural attitudes toward illness, and the fact that the disorder is neither life threatening nor contagious and does not have to be reported to any central authority makes it difficult to tell what the actual rates are in developing countries.

Symptoms of irritable bowel syndrome (IBS) include distended bowel and colonic spasms.

Symptoms of irritable bowel syndrome (IBS) include distended bowel and colonic spasms.


IBS involves both the large intestine (colon) and the small intestine. Symptoms include pain, cramping, and either constipation, diarrhea, or alternating periods of both. It is not contagious and is not strictly inherited, and despite the discomfort the bowel is structurally normal—no infection, no tumors or polyps, and no abnormalities in the cells lining the intestinal wall.

IBS should not be confused with inflammatory bowel disease (IBD). Inflammatory bowel diseases such as Crohn's disease and ulcerative colitis cause changes in the cells lining the wall of the intestine. These cell abnormalities can be seen in samples (biopsies) taken from the wall of the intestine. In a person who has IBS, cell samples taken from the lining of the intestine look normal. Inflammatory bowel diseases increase the risk of developing intestinal cancers; IBS does not.

Irritable bowel syndrome is not a life-threatening disorder and does not progress to a more serious disorder, but it is the cause of about one in every ten doctor visits in the United States. Its symptoms, although not medically serious, are varied, changeable, and intrusive enough to impact an individual's quality of life. IBS causes people to miss school or work and to avoid certain activities. It can also interfere with personal relationships.

Causes and symptoms

The cause of IBS is unknown. Some researchers believe that the bowel of people with IBS is inappropriately sensitive and overreacts to normal things such as the passage of food and stress. Other researchers suggest that there is a flaw in the way the brain and the gut interact. Some scientists suggest that an earlier infection predisposes some people to develop IBS. Others have found an abnormal numbers of receptors for the neurotransmitter serotonin in the gastrointestinal tract of people with IBS. Low doses of some antidepressant drugs that affect serotonin levels have been found to improve IBS symptoms in some people.

Whatever the cause, symptoms of IBS include pain or discomfort in the abdomen, feeling bloated (fullness) or having a lot of gas, and mucus in the stool as well as diarrhea, constipation, or alternating periods of both. The symptoms come and go, being present for a few days each month or lasting for around three months. They range from mild to severe (though most people have mild symptoms) and can change in a single individual over time. The impact of symptoms can also range from mild to severe, and the intensity of symptoms can also change over time. Symptoms are usually reduced or relieved by a bowel movement.

Although outside factors are not thought to cause IBS, certain things can trigger IBS symptoms. Triggers vary from person to person. Possible triggers include:

Celiac disease—
A digestive disease that causes damage to the small intestine. It results from the inability to digest gluten found in wheat, rye, and barley.
A medical examination of the large bowel and the distal part of the small bowel with a tiny CCD (charged-couple device) camera or an optical fiber camera attached to the end of a flexible tube.
An acronym for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols: short-chain carbohydrates that are difficult for the body to digest.
A combination of two proteins found in some cereal grains, such as wheat.
Chemicals that carry nerve impulses from one cell to another. Abnormal levels of specific neurotransmitters could make the bowel more reactive.
A sugar found in milk.
An enzyme that breaks down lactose.
Lactose tolerance test—
A test to measure how well the body processes lactose.
A neurotransmitter derived from the amino acid tryptophan, widely found within the tissues of the body.
A minimally invasive examination of the large intestine, going from the rectum to the last portion of the colon.


There are no tests for IBS. It is often diagnosed by ruling out other disorders with similar symptoms, such as ulcerative colitis. When other possible diseases have been eliminated through medical testing, IBS is diagnosed.

Another approach to diagnosis is to use the Rome criteria for diagnosis. Following these criteria, IBS is diagnosed if the symptoms of abdominal pain and diarrhea and/or constipation are present for at least 12 weeks (the weeks do not have to be consecutive) and several of the following conditions are met:

Often these two approaches to diagnosis are combined, and the physician may initially perform a sigmoidoscopy or a colonoscopy to look at the inside of the bowel. In these procedures, a tube called an endoscope is inserted through the rectum and into the colon. At the end of the endoscope is a tiny camera that allows the doctor to see if there is damage to the cells lining the digestive tract. During this procedure, the doctor also removes small tissue samples (biopsies) to look for abnormal cells under the microscope. This can eliminate inflammatory bowel syndrome as the cause of symptoms.

The doctor may also do a lactose intolerance test. Lactose is a sugar found in milk. People who lack the enzyme to break down this sugar have symptoms similar to those of irritable bowel syndrome. Lactose intolerance is common, and a lactose intolerance test can confirm or eliminate lactose as the source of the symptoms.

The doctor may also do a blood test to determine if symptoms are caused by early or mild celiac disease. People with celiac disease are sensitive to gluten, a protein found in wheat, barley, rye, and the products made from these grains. Eating foods containing gluten often causes symptoms similar to IBS in people with celiac disease.

Blood in the stool, vomiting, fever, and diarrhea that awakens a person at night are not symptoms of IBS. Individuals with these symptoms should see a doctor.


Treatment of IBS is aimed at relieving symptoms and falls into three categories: lifestyle adjustments, including diet; coping skills; and drug therapy. In the 2010s, many doctors and patients began considering the role of FODMAPs—fermentable oligosaccharides, disaccharides, monosaccharides, and polyols— in the diet.

Low-FODMAP diet

In the 2010s, experts found that restricting fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) was an effective method of treating IBS. FODMAPs are short-chain carbohydrates. Humans lack the enzymes to digest these carbohydrates, so they are not fully absorbed in the small intestine and instead drag water into the intestine where it can ferment and generate gases. Foods high in FODMAPs include wheat, rye, barley, onion, garlic, cruciferous vegetables such as cabbage and brussels sprouts, cauliflower, asparagus, beans, many fruits, and artificial sweeteners, such as sorbitol, xylitol, mannitol, and isomalt. Many people with IBS also have trouble digesting lactose and fructose.

Foods low in FODMAPs include meats, tofu, almonds and seeds, oranges, grapes, melons, hard cheeses, and vegetables, including lettuce, tomato, zucchini, bean sprouts and alfalfa sprouts, carrots, and cucumbers. Lactose-free dairy products and gluten-free breads and baked goods are also low in FODMAPs.

In January 2018, a study published in the United Kingdom provided guidelines for patients and medical professionals wishing to implement low-FODMAP diets. Designing the diet can be a multi-step process that involves assessing symptoms and experimenting with eliminating or adding specific foods to see if they make any difference to the patient.


Lifestyle adjustments include:

Learning new coping skills may involve psychotherapy (talk therapy) or professional counseling to help resolve problems that are causing stress or learning techniques to cope with stress. Some of these coping techniques include biofeedback, yoga, massage, meditation, deep breathing exercises, progressive relaxation exercises, and hypnosis.


Drug therapy depends on specific symptoms. Over-the-counter antidiarrheal products such as loperamide (Imodium) and diphenoxylate (Lomotil) can improve bowel movements and reduce the impact of IBS on daily activities. In addition, bile-acid–binding agents, such as cholestyramine (Questran), help to reduce bile acids from building up in the colon, which slows the passage of stool and relieves diarrhea.

Over-the-counter laxatives can be helpful in treating constipation but must be used sparingly, because regular use creates bowel dependence. Bulk-forming or fiber-supplement laxatives are generally considered the safest type of laxative. Some common brand names of fiber-supplement laxatives are Metamucil, Citrucel, Fiberall, Konsyl, and Serutan. These must be taken with water. They provide extra fiber that absorbs water and helps keep the stool soft. The extra bulk also helps move materials through the colon. Lubiprostone (Amitiza) is also used for constipation by helping to increase the fluid levels in the intestines, which allows the stool to pass more easily.

Stool softeners help prevent the stool from drying out. They are recommended for people who should not strain to have a bowel movement, such as people recovering from abdominal surgeries or childbirth. Brand names include Colace and Surfak. Stimulant laxatives, such as Dulcolax, Senokot, Correctol, and Purge, increase the rhythmic contractions of the colon and help to move the material along faster. They also help to reduce irritation within the lining of the intestines.

Lubricants add grease to the stool so that it moves more easily through the colon. Mineral oil is the most common lubricant. Saline laxatives, such as Milk of Magnesia, draw water from the body into the colon to help soften and move the stool.

Lubiprostone (Amitiza) is used to treat constipationtype IBS in both men and women. Lubiprostone causes the small intestine to secrete additional fluids, which helps stool pass more easily. Like alosetron, lubiprostone is only to be used in severe cases when all other treatment types have failed.

Tegaserod (Zelnorm), previously prescribed for severe constipation, was withdrawn from the U.S. market at the request of the FDA in March 2007 because of serious heart-related side effects.

Some people with IBS have seen their symptoms improve when they take low levels of tricyclic antidepressants that target serotonin levels in the brain. The dosage of these drugs is lower than that used to treat depression. Serotonin is a neurotransmitter that some researchers think plays a role in IBS. Newer selective serotonin reuptake inhibitor (SSRI) antidepressants seem to be less effective. People whose symptoms do not improve with lifestyle changes may want to talk to their doctor about this option and should also seek treatment for any accompanying depression or anxiety.

Nutrition and dietary concerns

The main dietary concern of people with constipation-type IBS has traditionally been increasing the amount of fiber in the diet. Insoluble fiber helps material move through the large intestine faster so that the body reabsorbs less water and the stool remains softer. Soluble fiber dissolves in water and forms a gel that keeps the stool soft. Additional health benefits include improvements in gut microbiome, lower cholesterol, glycemic control, and weight management. Good sources of fiber include apples with skin, dried beans, pears with skin, brown rice, oatmeal, and popcorn. Some of these foods, however, are high in FODMAPs; apples and pears, for example, are high in polyols. Many sources of information on IBS do yet not take FODMAPs into account. A patient seeking to reduce FODMAPs while increasing fiber will have to pay attention to this issue.


Every year, the symptoms of about 10% of people with IBS spontaneously disappear. The reason for this is not understood. For most people, however, IBS is a chronic disorder that lasts for a lifetime. Symptoms are erratic and changeable; there are periods when symptoms improve, and periods when symptoms worsen. For some people, the symptoms of IBS can adversely affect activities of daily life, such as going to school or work, attending social events, taking vacations, or running errands. IBS is not considered a symptom of any other disorder, and it does not cause permanent harm to the intestines or develop into more serious diseases.



Since the cause of IBS is unknown, the disorder cannot be prevented.

See also Celiac disease ; Constipation ; Crohn's disease ; CSIRO total wellbeing diet ; Digestive diseases ; Fiber ; Food sensitivities ; High-fiber diet ; Inflammatory bowel disease ; Irritable bowel syndrome diet ; Prebiotics and probiotics .



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American College of Gastroenterology, 6400 Goldsboro Rd., Ste. 200, Bethesda, MD, 20817, (301) 263-9000, .

American Gastroenterological Association, 4930 Del Ray Ave., Bethesda, MD, 20814, (301) 654-2055, (800) 877-1600, Fax: (301) 654-5920,, .

International Foundation for Functional Gastrointestinal Disorders, PO Box 170864, Milwaukee, WI, 53217-8076, (414) 964-1799, (888) 964-2001, Fax: (414) 964-7176,, .

Irritable Bowel Syndrome Self Help and Support Group, 24 Dixwell Ave., #118, New Haven, CT, 06511, (203) 424-0660, , .

Tish Davidson, AM
Revised by Amy Hackney Blackwell, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.