Irritable Bowel 

Syndrome 

National Digestive Diseases Information Clearinghouse 

U.S. Department 

of Health and 

Human Services 

NATIONAL 

INSTITUTES 

OF HEALTH 

What is irritable bowel 

syndrome (IBS)? 

Irritable bowel syndrome is a disorder 

characterized most commonly by cramping, 

abdominal pain, bloating, constipation, 

and diarrhea. IBS causes a great deal of 

discomfort and distress, but it does not permanently harm the intestines and does not 

lead to a serious disease, such as cancer. 

Most people can control their symptoms 

with diet, stress management, and prescribed medications. For some people, 

however, IBS can be disabling. They may 

be unable to work, attend social events, 

or even travel short distances. 

As many as 20 percent of the adult population, or one in five Americans, have 

symptoms of IBS, making it one of the 

most common disorders diagnosed by 

doctors. It occurs more often in women 

than in men, and it begins before the age 

of 35 in about 50 percent of people. 

What are the symptoms 

of IBS? 

Abdominal pain, bloating, and discomfort 

are the main symptoms of IBS. However, 

symptoms can vary from person to person. 

Some people have constipation, which 

means hard, difficult­to­pass, or infrequent 

bowel movements. Often these people 

report straining and cramping when trying 

to have a bowel movement but cannot 

eliminate any stool, or they are able to 

eliminate only a small amount. If they are 

able to have a bowel movement, it may 

have mucus in it, which is a fluid that moistens and protects passages in the digestive 

system. Some people with IBS experience 

diarrhea, which is frequent, loose, watery 

stools. People with diarrhea frequently feel 

an urgent and uncontrollable need to have 

a bowel movement. Other people with 

IBS alternate between constipation and 

diarrhea. Sometimes people find that their 

symptoms subside for a few months and 

then return, while others report a constant 

worsening of symptoms over time. 

Liver 

Small 

intestine 

Colon 

(shaded) 

Stomach 

Rectum 

Anus 

The colon and rectum are the two main parts of the 

large intestine. 
 

	 	 	 	 	

	 	 	 	 	 	 	

	 	 	 	 	

	 	 	 	 	

	 	 	 	 		 	

	 	 	 	 	

	 	 	 	 	 	

	 	 	 	 	 	

	 	 	 	 	

What causes IBS? 

Researchers have yet to discover any specific cause for IBS. One theory is that 

people who suffer from IBS have a colon 

that is particularly sensitive and reactive 

to certain foods and stress. The immune 

system, which fights infection, may also be 

involved. 

•	 Normal motility, or movement, may

not be present in the colon of a person 

who has IBS. It can be spasmodic or 

can even stop working temporarily. 

Spasms are sudden strong muscle 

contractions that come and go. 

•	 The lining of the colon called the

epithelium, which is affected by the 

immune and nervous systems, regulates the flow of fluids in and out of 

the colon. In IBS, the epithelium 

appears to work properly. However, 

when the contents inside the colon 

move too quickly, the colon loses its 

ability to absorb fluids. The result is 

too much fluid in the stool. In other 

people, the movement inside the 

colon is too slow, which causes extra 

fluid to be absorbed. As a result, a 

person develops constipation. 

•	 A person’s colon may respond

strongly to stimuli such as certain 

foods or stress that would not bother 

most people. 

•	 Recent research has reported that

serotonin is linked with normal gastrointestinal (GI) functioning. Serotonin 

is a neurotransmitter, or chemical, 

that delivers messages from one part 

of the body to another. Ninety-five

percent of the serotonin in the body is 

located in the GI tract, and the other 

5 percent is found in the brain. Cells 

that line the inside of the bowel work 

as transporters and carry the serotonin out of the GI tract. People with 

IBS, however, have diminished receptor activity, causing abnormal levels 

of serotonin to exist in the GI tract. 

As a result, they experience problems 

with bowel movement, motility, and 

sensation—having more sensitive pain 

receptors in their GI tract. 

•	 Researchers have reported that IBS

may be caused by a bacterial infection 

in the gastrointestinal tract. Studies 

show that people who have had gastroenteritis sometimes develop IBS, 

otherwise called post­infectious IBS. 

•	 Researchers have also found very mild

celiac disease in some people with 

symptoms similar to IBS. People with 

celiac disease cannot digest gluten, 

a substance found in wheat, rye, and 

barley. People with celiac disease cannot eat these foods without becoming 

very sick because their immune system responds by damaging the small 

intestine. A blood test can determine 

whether celiac disease may be present. 

(For information about celiac disease, 

see the National Institute of Diabetes

and Digestive and Kidney Diseases’

[NIDDK’s] Celiac Disease fact sheet.) 

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How is IBS diagnosed? 

IBS is generally diagnosed on the basis of 

a complete medical history that includes 

a careful description of symptoms and a 

physical examination. 

No specific test for IBS exists, although

diagnostic tests may be performed to rule 

out other problems. These tests may 

include stool sample testing, blood tests, 

and x rays. Typically, a doctor will perform 

a sigmoidoscopy or colonoscopy, which 

allows the doctor to look inside the colon 

by inserting a small, flexible tube with a 

camera on the end of it through the anus. 

The camera then transfers the images of 

the colon onto a large screen for the doctor 

to see better. 

If test results are negative, the doctor may 

diagnose IBS based on symptoms, including how often a person has had abdominal 

pain or discomfort during the past year, 

when the pain starts and stops in relation to bowel function, and how bowel 

frequency and stool consistency have 

changed. Many doctors refer to a list of 

specific symptoms that must be present 

to make a diagnosis of IBS. 

Symptoms include 

•	 Abdominal pain or discomfort for

at least 12 weeks out of the previous 

12 months. These 12 weeks do not 

have to be consecutive. 

•	 The abdominal pain or discomfort has

two of the following three features: 

–	 It is relieved by having a bowel 

movement. 

–	 When it starts, a change occurs 

in how often a person has a bowel 

movement. 

–	 When it starts, a change occurs 

in the form of the stool or the way 

it looks. 

•	 Certain symptoms must also be

present, such as 

–	 a change in frequency of bowel 

movements 

–	 a change in appearance of bowel 

movements 

–	 feelings of uncontrollable urgency 

to have a bowel movement 

–	 difficulty or inability to pass stool 

–	 mucus in the stool 

–	 bloating 

•	 Bleeding, fever, weight loss, and persistent severe pain are not symptoms 

of IBS and may indicate other problems such as inflammation or, rarely, 

cancer. 

The following have been associated with a 

worsening of IBS symptoms 

•	 large meals

•	 bloating from gas in the colon

•	 medicines

•	 wheat, rye, barley, chocolate, milk

products, or alcohol 

•	 drinks with caffeine, such as coffee,

tea, or colas 

•	 stress, conflict, or emotional upsets

Researchers have found that women with 

IBS may have more symptoms during 

their menstrual periods, suggesting that 

reproductive hormones can worsen IBS 

problems. 

In addition, people with IBS frequently suffer from depression and anxiety, which can 

worsen symptoms. Similarly, the symptoms 

associated with IBS can cause a person to 

feel depressed and anxious. 

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What is the treatment 

for IBS? 

Unfortunately, many people suffer from 

IBS for a long time before seeking medical 

treatment. Up to 70 percent of people 

suffering from IBS are not receiving 

medical care for their symptoms. No cure

has been found for IBS, but many options 

are available to treat the symptoms. The 

doctor will prescribe the best treatments 

for a person’s particular symptoms and

encourage the person to manage stress and 

make dietary changes. 

Medications are an important part of 

relieving symptoms. The doctor may 

suggest fiber supplements or laxatives for 

constipation or medicines to decrease 

diarrhea, such as diphenoxylate and atropine (Lomotil) or loperamide (Imodium). 

An antispasmodic is commonly prescribed, which helps control colon muscle 

spasms and reduce abdominal pain. Antidepressants may relieve some symptoms. 

However, both antispasmodics and antidepressants can worsen constipation, so some 

doctors will also prescribe medications that 

relax muscles in the bladder and intestines, 

such as belladonna alkaloid combinations 

and phenobarbital (Donnatal) and chlordiazepoxide and clidinium bromide (Librax). 

These medications contain a mild sedative, 

which can be habit forming, so they need to 

be used under the guidance of a physician. 

A medication available specifically to treat 

IBS is alosetron hydrochloride (Lotronex). 

Lotronex has been reapproved with significant restrictions by the U.S. Food and 

Drug Administration (FDA) for women

with severe IBS who have not responded to 

conventional therapy and whose primary 

symptom is diarrhea. However, even in 

these patients, Lotronex should be used 

with great caution because it can have serious side effects such as severe constipation 

or decreased blood flow to the colon. 

With any medication, even over­thecounter medications such as laxatives 

and fiber supplements, it is important to 

follow the doctor’s instructions. Some people report a worsening in abdominal bloating and gas from increased fiber intake, and 

laxatives can be habit forming if they are 

used too frequently. 

Medications affect people differently, 

and no one medication or combination 

of medications will work for everyone 

with IBS. Working with the doctor to 

find the best combination of medicine, 

diet, counseling, and support to control 

symptoms may be helpful. 

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How does stress affect IBS? 

Stress—feeling mentally or emotionally 

tense, troubled, angry, or overwhelmed— 

can stimulate colon spasms in people with 

IBS. The colon has many nerves that connect it to the brain. Like the heart and the 

lungs, the colon is partly controlled by the 

autonomic nervous system, which responds 

to stress. These nerves control the normal contractions of the colon and cause 

abdominal discomfort at stressful times. 

People often experience cramps or “butterflies” when they are nervous or upset. 

In people with IBS, the colon can be overly 

responsive to even slight conflict or stress. 

Stress makes the mind more aware of the 

sensations that arise in the colon, making 

the person perceive these sensations as 

unpleasant. 

Some evidence suggests that IBS is affected 

by the immune system, which fights infection in the body. The immune system is 

affected by stress. For all these reasons, 

stress management is an important part 

of treatment for IBS. Stress management 

options include 

•	 stress reduction training and relaxation

therapies such as meditation 

•	 counseling and support

•	 regular exercise such as walking

or yoga 

•	 changes to the stressful situations in a

person’s life

•	 adequate sleep

What does the colon do? 

The colon, which is about 5 feet long, 

connects the small intestine to the rectum and anus. The major function of 

the colon is to absorb water, nutrients, 

and salts from the partially digested 

food that enters from the small intestine. Two pints of liquid matter enter 

the colon from the small intestine each 

day. Stool volume is a third of a pint. 

The difference between the amount 

of fluid entering the colon from the 

small intestine and the amount of stool 

in the colon is what the colon absorbs 

each day. 

Colon motility—the contraction of the 

colon muscles and the movement of 

its contents—is controlled by nerves, 

hormones, and impulses in the colon 

muscles. These contractions move the 

contents inside the colon toward the 

rectum. During this passage, water

and nutrients are absorbed into the 

body, and what is left over is stool. A 

few times each day contractions push 

the stool down the colon, resulting in a 

bowel movement. However, if the muscles of the colon, sphincters, and pelvis 

do not contract in the right way, the 

contents inside the colon do not move 

correctly, resulting in abdominal pain, 

cramps, constipation, a sense of incomplete stool movement, or diarrhea. 

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Can changes in diet 

help IBS? 

For many people, careful eating reduces 

IBS symptoms. Before changing the diet, 

keep a journal noting the foods that seem 

to cause distress. Then discuss these findings with the doctor. A registered dietitian 

can help a person make changes to the diet. 

For instance, if dairy products cause symptoms to flare up, try eating less of those 

foods. A person might be able to tolerate 

yogurt better than other dairy products 

because it contains bacteria that supply the 

enzyme needed to digest lactose, the sugar 

found in milk products. Dairy products

are an important source of calcium and 

other nutrients. If a person needs to avoid 

dairy products, adequate nutrients should 

be added in foods or supplements should 

be taken. 

In many cases, dietary fiber may lessen 

IBS symptoms, particularly constipation. 

However, it may not help with lowering 

pain or decreasing diarrhea. Whole grain 

breads and cereals, fruits, and vegetables 

are good sources of fiber. High­fiber diets 

keep the colon mildly distended, which 

may help prevent spasms. Some forms 

of fiber keep water in the stool, thereby 

preventing hard stools that are difficult to 

pass. Doctors usually recommend a diet

with enough fiber to produce soft, painless 

bowel movements. High­fiber diets may 

cause gas and bloating, although some 

people report that these symptoms go away 

within a few weeks. Increasing fiber intake 

by 2 to 3 grams per day will help reduce the 

risk of increased gas and bloating. 

Drinking six to eight glasses of plain water

a day is important, especially if a person has 

diarrhea. Drinking carbonated beverages,

such as sodas, may result in gas and cause 

discomfort. Chewing gum and eating too 

quickly can lead to swallowing air, which 

also leads to gas. 

Large meals can cause cramping and diarrhea, so eating smaller meals more often, 

or eating smaller portions, may help IBS 

symptoms. Eating meals that are low in fat 

and high in carbohydrates such as pasta; 

rice; whole­grain breads and cereals, unless 

a person has celiac disease; fruits; and vegetables may help. 

Is IBS linked to other 

health problems? 

As its name indicates, IBS is a syndrome—a 

combination of signs and symptoms. IBS 

has not been shown to lead to a serious 

disease, including cancer. Through the 

years, IBS has been called by many names, 

among them colitis, mucous colitis, spastic colon, or spastic bowel. However, no 

link has been established between IBS 

and inflammatory bowel diseases such as 

Crohn’s disease or ulcerative colitis.

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Points to Remember 

•	 IBS is a disorder that interferes with

the normal functions of the colon. 

The symptoms are crampy abdominal pain, bloating, constipation, and 

diarrhea. 

•	 IBS is a common disorder found

more often in women than men. 

•	 People with IBS have colons that are

more sensitive and reactive to things 

that might not bother other people, 

such as stress, large meals, gas, 

medicines, certain foods, caffeine, 

or alcohol. 

•	 IBS is diagnosed by its signs and

symptoms and by the absence of 

other diseases. 

•	 Most people can control their symptoms by taking medicines such as 

laxatives, antidiarrhea medicines, 

antispasmodics, or antidepressants; 

reducing stress; and changing their 

diet. 

•	 IBS does not harm the intestines

and does not lead to cancer. It is 

not related to Crohn’s disease or

ulcerative colitis. 

Hope through Research 

The NIDDK conducts and supports

research into many kinds of digestive 

disorders including IBS. Researchers 

are studying gastrointestinal motility and 

sensitivity to find possible treatments for 

IBS. These studies include the structure 

and contraction of gastrointestinal muscles, 

as well as the mechanics of fluid movement 

through the intestines. Understanding the 

influence of the nerves, hormones, and 

inflammation in IBS may lead to new treatments to better control the symptoms. 

Participants in clinical trials can play a 

more active role in their own health care, 

gain access to new research treatments 

before they are widely available, and help 

others by contributing to medical research. 

For information about current studies, visit 

www.ClinicalTrials.gov. 

The U.S. Government does not endorse or favor any 

specific commercial product or company. Trade, 

proprietary, or company names appearing in this 

document are used only because they are considered 

necessary in the context of the information provided. 

If a product is not mentioned, the omission does not 

mean or imply that the product is unsatisfactory. 

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For More Information 

International Foundation for Functional 

Gastrointestinal Disorders 

P.O. Box 170864 

Milwaukee, WI 53217–8076 

Phone: 1–888–964–2001 

Fax: 414–964–7176 

Email: iffgd@iffgd.org 

Internet: www.iffgd.org 

Acknowledgments 

Publications produced by the Clearinghouse are carefully reviewed by both 

NIDDK scientists and outside experts.

You may also find additional information about this 

topic by visiting MedlinePlus at www.medlineplus.gov. 

This publication may contain information about 

medications. When prepared, this publication 

included the most current information available. 

For updates or for questions about any medications, 

contact the U.S. Food and Drug Administration

toll-free at 1–888–INFO–FDA (1–888–463–6332) or

visit www.fda.gov. Consult your doctor for more 

information. 

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2 Information Way 

Bethesda, MD 20892–3570

Phone: 1–800–891–5389 

TTY: 1–866–569–1162 

Fax: 703–738–4929 

Email: nddic@info.niddk.nih.gov 

Internet: www.digestive.niddk.nih.gov 

The National Digestive Diseases

Information Clearinghouse (NDDIC)

is a service of the National Institute

of Diabetes and Digestive and Kidney

Diseases (NIDDK). The NIDDK

is part of the National Institutes of Health

of the U.S. Department of Health and

Human Services. Established in 1980, the 

Clearinghouse provides information about 

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disorders and to their families, health 

care professionals, and the public. The 

NDDIC answers inquiries, develops and

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with professional and patient organizations 

and Government agencies to coordinate 

resources about digestive diseases. 

This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired. 

This publication is available at 

www.digestive.niddk.nih.gov. 

U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES 

National Institutes of Health 

NIH Publication No. 07–693 

September 2007