Irritable bowel syndrome (IBS) is a disorder of the entire digestive tract that causes abdominal pain and constipation or diarrhea.
IBS affects about 10 to 15% of 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).
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. Although the normal functioning is impaired, there are no structural abnormalities that can be seen with an endoscope (a flexible viewing tube), x-rays, or blood tests. Thus, IBS is identified by the characteristics of the symptoms and, when needed, the results of limited tests.
The cause of IBS 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 that do, the abnormal contractions do not always coincide with symptoms.
Emotional factors (for example, stress, anxiety, depression, and fear), diet, drugs, hormones, or minor irritants may trigger or worsen a flare-up (a bout or attack) of IBS. For some people, high-calorie meals or a high-fat diet may be a trigger (precipitating factor). For other people, wheat, dairy products, coffee, tea, or citrus fruits seem to aggravate the symptoms. Because many food products contain several ingredients, it may be difficult to identify the specific trigger. Others find that eating too quickly or eating after too long a period without food stimulates a flare-up. However, the relationship is inconsistent. A person does 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.
IBS tends to begin in the teens and 20s, causing bouts of symptoms that recur at irregular periods. Onset 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.
Symptoms include abdominal pain related to or relieved by having a bowel movement (defecation), change in stool frequency (such as constipation or diarrhea) or consistency, abdominal expansion (distention), mucus in the stool, and the sensation of incomplete emptying after defecation. The pain may come in bouts of continuous dull aching or cramps, usually over the lower abdomen. Bloating, gas, nausea, headaches, fatigue, depression, anxiety, and difficulty concentrating are other possible symptoms. 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.
Most people with IBS appear healthy. A physical examination generally does not reveal anything unusual except sometimes tenderness over the large intestine. Doctors usually perform some tests—for example, blood tests, a stool examination, and a sigmoidoscopy (see Diagnosis of Digestive Disorders: Endoscopy)—to differentiate IBS from Crohn's disease, ulcerative colitis, cancer (mainly in people over age 40), collagenous colitis, lymphocytic colitis, and the many other diseases that can cause abdominal pain and changes in bowel habits. These test results are usually normal in people with IBS, although the stool may be watery, and the sigmoidoscopy procedure may cause an unusual amount of spasms and pain. Doctors usually perform more tests—such as abdominal ultrasound, x-rays of the intestines, or a colonoscopy (see Diagnosis of Digestive Disorders: Endoscopy)—in older people and in those who have symptoms that are unusual for IBS, such as fever, bloody stools, weight loss, and vomiting.
Other digestive tract disorders (such as appendicitis, gallbladder disease, ulcers, and cancer) may develop in a person with IBS, particularly after age 40. Thus, if a person's symptoms change significantly or are unusual for IBS, further testing may be needed.
Treatment 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.
In general, a normal diet is best. Many people do better eating frequent, smaller meals rather than less frequent, larger meals (for example, five or six small meals rather than three large meals a day). People with bloating and increased gas (flatulence) should avoid beans, cabbage, and other foods that are difficult to digest. Sorbitol, an artificial sweetener used in dietetic foods and in some 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. A low-fat diet helps some people, particularly those whose stomach empties too slowly or too quickly. People who have both IBS and lactase deficiency should consume dairy products in moderation. Even patients with lactase deficiency can probably tolerate a glass of milk consumed in small amounts during the day.
Constipation can often be relieved by eating more fiber. People with constipation can take a tablespoon of raw bran with plenty of water and other fluids at each meal, or they 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 often effective and reasonably safe. Such laxatives include those containing sorbitol, lactulose, or polyethylene glycol, and stimulant laxatives such as those containing bisacodyl or glycerin. Lubiprostone, a newer laxative, may also relieve constipation.
Smooth-muscle relaxants, such as dicyclomine, can relieve abdominal pain but often cause anticholinergic side effects (see see Aging and Drugs: 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, as may drugs such as alosetron, which decrease the effects of serotonin, a chemical messenger in the body. Aromatic oils, such as oil of peppermint, often help symptoms of flatulence and cramping. Antidepressants, behavior modification techniques (such as cognitive-behavioral therapy), psychotherapy, and hypnosis are often extremely effective for managing symptoms of IBS. Long-term use of antidepressants in low or higher doses is reasonably safe. Antidepressants may not only relieve pain and other symptoms but also may help relieve sleep problems and depression or anxiety.
Last full review/revision May 2007 by Adil E. Bharucha, MBBS, MD