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Irritable Bowel Syndrome (IBS)


Stephanie M. Moleski

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

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

Irritable bowel syndrome is a disorder of the digestive tract that causes recurring abdominal pain and constipation or diarrhea.

  • Symptoms vary but often include lower abdominal pain, bloating, gas, and constipation or diarrhea.

  • A variety of substances and emotional factors can trigger symptoms of irritable bowel syndrome.

  • A doctor usually diagnoses irritable bowel syndrome based on the symptoms but does tests to rule out other problems.

  • Diet modification and drugs can usually relieve specific symptoms.

Irritable bowel syndrome (IBS) is common among the general population. Some but not all studies suggest women with IBS are more likely to consult a doctor. IBS is the most common disorder diagnosed by gastroenterologists (doctors who specialize in disorders of the digestive tract) and is a common reason why many people visit their primary care physician.

IBS is generally classified as a functional disorder because it impairs the functioning of the body’s normal activities, such as the movement of the intestines, the sensitivity of the nerves of the intestines, or the way in which the brain controls some of these functions. However, although the normal functioning is impaired, there are no structural abnormalities that can be found with an endoscope (a flexible viewing tube), x-rays, biopsies, or blood tests. Thus, IBS is identified by the characteristics of the symptoms and, when done, normal results of tests.

Causes of IBS

The cause of irritable bowel syndrome is not clear. In many people with IBS, the digestive tract is especially sensitive to many stimuli. People may experience discomfort caused by intestinal gas or contractions that other people do not find distressing. Although the changes in bowel movements that occur with IBS might seem to be related to abnormal intestinal contractions, not all people with IBS have abnormal contractions, and in many of those who do, the abnormal contractions do not always coincide with symptoms. In some people, symptoms of IBS begin after an episode of gastroenteritis Gastroenteritis .

For some people, high-calorie meals or a high-fat diet may be a trigger.

For other people, wheat, dairy products, beans, chocolate, coffee, tea, some artificial sweeteners, certain vegetables (such as asparagus or broccoli), or stone fruits (such as apricots) seem to aggravate the symptoms. These foods contain carbohydrates that are poorly absorbed by the small intestine. The carbohydrates become fermented by bacteria in the intestine, which causes gas, bloating, and cramping. Because many food products contain several ingredients, it may be difficult to identify the specific trigger.

Other people find that eating too quickly or eating after too long a period without food stimulates a flare-up (a bout or attack). However, the relationship is inconsistent.

Emotional factors (for example, stress, anxiety, depression, and fear), diet, drugs (including laxatives), hormones, or minor irritants may trigger or worsen a flare-up of IBS.

People do not always get symptoms after a usual trigger, and symptoms often appear without any obvious trigger. It is not clear how all the triggers relate to the cause of IBS.

Symptoms of IBS

IBS tends to begin in adolescence and the 20s, causing bouts of symptoms that come and go at irregular periods. The start of IBS symptoms in late adult life is less common but not rare. Flare-ups almost always occur when a person is awake, and they rarely wake a person from sleep.

In general, the character and location of pain, triggers, and the pattern of bowel movements are relatively consistent over time. However, symptoms may increase or decrease in severity and also change over time.

Diagnosis of IBS

  • A doctor's evaluation based on the Rome criteria

  • Laboratory and imaging tests to look for other disorders

Most people with IBS appear healthy. Doctors base the diagnosis of irritable bowel syndrome on the characteristics of the person's symptoms. Doctors also use standardized symptom-based criteria for diagnosing IBS called the Rome criteria. They may also do tests to diagnose common illnesses that can cause similar symptoms, particularly when people are over 40 or have warning signs such as fever, weight loss, rectal bleeding, or vomiting.

Doctors use the Rome criteria to diagnose IBS in people who have had abdominal pain for at least 1 day a week in the last 3 months along with 2 or more of the following:

  • Pain that is related to defecation.

  • Pain is associated with a change in stool frequency (constipation or diarrhea).

  • Pain is associated with a change in the consistency of stool.

A physical examination generally does not reveal anything unusual except sometimes tenderness over the large intestine. Doctors do a digital rectal examination, in which a gloved finger is inserted in the person's rectum. Women also undergo a pelvic examination Gynecologic Examination For gynecologic care, a woman should choose a health care practitioner with whom she can comfortably discuss sensitive topics, such as sex, birth control, pregnancy, and problems related to... read more .

Doctors usually do more tests, such as ultrasonography Ultrasound Scanning (Ultrasonography) of the Abdomen Ultrasound scanning uses sound waves to produce pictures of internal organs ( see also Ultrasonography). An ultrasound scan can show the size and shape of many organs, such as the liver and... read more Ultrasound Scanning (Ultrasonography) of the Abdomen of the abdomen, x-rays X-Ray Studies of the Digestive Tract X-rays often are used to evaluate digestive problems. Standard x-rays (plain x-rays) do not require any special preparation ( see Plain X-Rays). These x-rays usually can show a blockage or paralysis... read more of the intestines, or a colonoscopy Endoscopy Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). Endoscopy can also be used to treat many disorders because doctors are able to pass instruments... read more , in older people and in people who have symptoms that are unusual for IBS, such as fever, bloody stools, weight loss, and vomiting. Doctors may do a test to rule out lactose intolerance Lactose Intolerance Lactose intolerance is the inability to digest the sugar lactose because of a lack of the digestive enzyme lactase, leading to diarrhea and abdominal cramping. Lactose intolerance is caused... read more or bacterial overgrowth Small Intestinal Bacterial Overgrowth (SIBO) Small intestinal bacterial overgrowth is a disorder in which poor movement of intestinal contents allows certain normal intestinal bacteria to grow excessively, causing diarrhea and poor absorption... read more and also ask questions to rule out laxative abuse.

Because IBS symptoms can be triggered by stress and emotional conflicts, doctors ask questions to help identify stress, anxiety, or mood disorders.

Treatment of IBS

  • Eating a normal diet and avoiding gas-producing and diarrhea-producing foods

  • Increasing fiber and water intake for constipation

  • Sometimes drugs

Treatment of irritable bowel syndrome differs from person to person. If particular foods or types of stress appear to bring on the problem, they should be avoided if possible. For most people, especially those who tend to be constipated, regular physical activity helps keep the digestive tract functioning normally.


(For more information about diet and IBS, see these recommendations from the National Institute of Diabetes and Digestive Disease.)

Many people do better eating frequent, smaller meals rather than less frequent, larger meals (for example, 5 or 6 small meals rather than 3 large meals a day). People should try to slow their pace while eating. People with bloating and increased gas (flatulence) should avoid beans, cabbage, and other foods that are difficult to digest.

Some people find relief from IBS symptoms by restricting their intake of foods that are high in certain carbohydrates Carbohydrates, Proteins, and Fats Carbohydrates, proteins, and fats are the main types of macronutrients in food (nutrients that are required daily in large quantities). They supply 90% of the dry weight of the diet and 100%... read more called fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These foods are collectively called FODMAPs. FODMAPs are carbohydrates that are poorly absorbed and rapidly fermented by bacteria in the small intestine, leading to increased gas and discomfort.

Sorbitol, an artificial sweetener used in some foods, drugs, and chewing gums, should not be consumed in large amounts. Fructose, a sugar found in fruits, berries, and some plants, should be eaten only in small amounts. People who have IBS and who cannot digest the sugar lactose (called lactose intolerance Lactose Intolerance Lactose intolerance is the inability to digest the sugar lactose because of a lack of the digestive enzyme lactase, leading to diarrhea and abdominal cramping. Lactose intolerance is caused... read more ), which is found in milk and other dairy products, should consume dairy products in moderation.

People can try reducing their intake of the foods mentioned above one at a time and noting whether their symptoms change, or they can try a low-FODMAP diet, which restricts all of these foods.

A low-fat diet helps some people, particularly those whose stomach empties too slowly or too quickly.

Constipation can often be relieved by eating more fiber and drinking more water. People with constipation can take psyllium mucilloid supplements with two glasses of water. Increasing the dietary fiber may aggravate flatulence and bloating. Occasionally, such flatulence may be reduced by switching to a synthetic fiber preparation (such as methylcellulose).


Certain laxatives are reasonably safe and often effective for people with constipation. Such laxatives include those containing sorbitol, lactulose, or polyethylene glycol, and stimulant laxatives such as those containing bisacodyl or glycerin. The prescription laxative drugs lubiprostone, linaclotide, and plecanatide may also relieve constipation. Prucalopride is another drug that may help people who have chronic constipation.

Anticholinergic drugs, such as hyoscyamine, can relieve abdominal pain by blocking spasms of the intestinal muscles. However, these drugs often cause anticholinergic side effects ( see Anticholinergic: What Does It Mean? Anticholinergic: What Does It Mean? Anticholinergic: What Does It Mean? ), such as dry mouth, blurred vision, or difficulty urinating.

Antidiarrheal drugs, such as diphenoxylate or loperamide, help people with diarrhea. Alosetron, which decreases the effects of serotonin (a chemical messenger in the body), may be given to some women whose diarrhea caused by IBS cannot be managed with other drugs. However, because it has been associated with increasing the risk of ischemic colitis, its use is restricted. Eluxadoline is another drug that may be given to some people who have severe diarrhea caused by IBS.

The antibiotic rifaximin may be prescribed to relieve symptoms of diarrhea, bloating, and abdominal pain.

Antidepressants help relieve symptoms of abdominal pain as well as diarrhea and bloating in many people. Long-term use of certain antidepressants such as nortriptyline or desipramine is often helpful. Antidepressants may not only relieve pain and other symptoms but also may help relieve sleep problems and depression or anxiety.

Probiotics, which are bacteria naturally found in the body that promote the growth of good bacteria, may alleviate IBS symptoms, particularly bloating. Aromatic oils, such as oil of peppermint, often help relieve pain caused by cramps in some people.

Other treatments

More Information about IBS

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

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