Irritable Bowel 

Syndrome

National Digestive Diseases Information Clearinghouse

What is irritable bowel 

syndrome (IBS)?

Irritable bowel syndrome is a functional 

gastrointestinal (GI) disorder, meaning 

symptoms are caused by changes in how the 

GI tract works. People with a functional GI 

disorder have frequent symptoms; however, 

the GI tract does not become damaged. IBS 

is a group of symptoms that occur together, 

not a disease. In the past, IBS was called 

colitis, mucous colitis, spastic colon, nervous 

colon, and spastic bowel. The name was 

changed to reflect the understanding that 

the disorder has both physical and mental 

causes and is not a product of a person’s 

imagination.

IBS is diagnosed when a person has had 

abdominal pain or discomfort at least three 

times a month for the last 3 months without 

other disease or injury that could explain 

the pain. The pain or discomfort of IBS 

may occur with a change in stool frequency 

or consistency or be relieved by a bowel 

movement.

IBS is often classified into four subtypes 

based on a person’s usual stool consistency. 

These subtypes are important because they 

affect the types of treatment that are most 

likely to improve the person’s symptoms. 

The four subtypes of IBS are

•	 IBS with constipation (IBS-C) 

– hard or lumpy stools at least 

25 percent of the time

– loose or watery stools less than 

25 percent of the time

•	 IBS with diarrhea (IBS-D) 

– loose or watery stools at least 

25 percent of the time

– hard or lumpy stools less than 

25 percent of the time

•	 Mixed IBS (IBS-M) 

– hard or lumpy stools at least 

25 percent of the time

– loose or watery stools at least 

25 percent of the time

•	 Unsubtyped IBS (IBS-U) 

– hard or lumpy stools less than 

25 percent of the time

– loose or watery stools less than 

25 percent of the time
2 Irritable Bowel Syndrome

What is the GI tract?

The GI tract is a series of hollow organs 

joined in a long, twisting tube from the 

mouth to the anus—the opening through 

which stool leaves the body. Food is digested 

by the movement of muscles in the GI tract, 

along with the release of hormones and 

enzymes. Organs that make up the GI tract 

are the mouth, esophagus, stomach, small 

intestine, large intestine—which includes the 

appendix, cecum, colon, and rectum—and 

anus. The intestines are sometimes called 

the bowel. The last part of the GI tract—

called the lower GI tract—consists of the 

large intestine and anus.

The large intestine absorbs water and any 

remaining nutrients from partially digested 

food passed from the small intestine. The 

large intestine then changes waste from 

liquid to a solid matter called stool. Stool 

passes from the colon to the rectum. The 

rectum is located between the last part of 

the colon—called the sigmoid colon—and 

the anus. The rectum stores stool prior 

to a bowel movement. During a bowel 

movement, stool moves from the rectum to 

the anus.

Large 

intestine

Esophagus

Stomach

Small 

intestine

Mouth

Appendix

Rectum Anus

The organs of the GI tract
3 Irritable Bowel Syndrome

How common is IBS and 

who is affected?

Studies estimate IBS affects 3 to 20 percent 

of the adult population, with most studies 

ranging from 10 to 15 percent.1 However, 

only 5 to 7 percent of the adult population 

has been diagnosed with the condition.2 IBS 

affects about twice as many women as men 

and is most often found in people younger 

than age 45.1

1Grundmann O, Yoon SL. Irritable bowel syndrome: 

epidemiology, diagnosis, and treatment: an update for 

health-care practitioners. Journal of Gastroenterology 

and Hepatology. 2010;25:691–699.

2Understanding irritable bowel syndrome. American 

College of Gastroenterology website. www.patients.

gi.org/gi-health-and-disease/understanding-irritablebowel-syndrome. Accessed August 15, 2013.

What are the symptoms 

of IBS?

The most common symptoms of IBS are 

abdominal pain or discomfort, often reported 

as cramping, along with changes in bowel 

habits. To meet the definition of IBS, the 

pain or discomfort will be associated with at 

least two of the following three symptoms:

•	 bowel movements that occur more or 

less often than usual

•	 stool that appears less solid and more 

watery, or harder and more lumpy, than 

usual

•	 bowel movements that improve the 

discomfort

Other symptoms of IBS may include

•	 diarrhea—having loose, watery stools 

three or more times a day and feeling 

urgency to have a bowel movement.

•	 constipation—having fewer than three 

bowel movements a week. During a 

bowel movement, stools can be hard, 

dry, and small, making them difficult to 

pass. Some people find it painful and 

often have to strain to have a bowel 

movement.

•	 feeling that a bowel movement is 

incomplete.

•	 passing mucus—a clear liquid made by 

the intestines that coats and protects 

tissues in the GI tract.

•	 abdominal bloating.

Symptoms may often occur after eating 

a meal. To meet the definition of IBS, 

symptoms must occur at least three times a 

month.

What causes IBS?

The causes of IBS are not well understood. 

Researchers believe a combination of 

physical and mental health problems can 

lead to IBS. 

Brain-Gut Signal Problems

Signals between the brain and nerves of the 

small and large intestines, also called the gut, 

control how the intestines work. Problems 

with brain-gut signals may cause IBS 

symptoms, such as changes in bowel habits 

and pain or discomfort.

GI Motor Problems

Normal motility, or movement, may not be 

present in the colon of a person who has IBS. 

Slow motility can lead to constipation and 

fast motility can lead to diarrhea. Spasms, 

or sudden, strong muscle contractions that 

come and go, can cause abdominal pain. 

Some people with IBS also experience 

hyperreactivity—a dramatic increase in 

bowel contractions in response to stress or 

eating.
4 Irritable Bowel Syndrome

Hypersensitivity

People with IBS have a lower pain threshold 

for bowel stretching caused by gas or stool 

compared with people who do not have IBS. 

The brain may process pain signals from the 

bowel differently in people with IBS.

Mental Health Problems

Mental health, or psychological, problems 

such as panic disorder, anxiety, depression, 

and post-traumatic stress disorder are 

common in people with IBS. The link 

between these disorders and development of 

IBS is unclear. GI disorders, including IBS, 

are often found in people who have reported 

past physical or sexual abuse. Researchers 

believe people who have been abused tend to 

express psychological stress through physical 

symptoms.

Bacterial Gastroenteritis

Some people who have bacterial 

gastroenteritis—an infection or irritation 

of the stomach and intestines caused by 

bacteria—develop IBS. Researchers do 

not know why gastroenteritis leads to IBS 

in some people and not others, though 

abnormalities of the GI tract lining and 

psychological problems may be factors.

Small Intestinal Bacterial 

Overgrowth 

Normally, few bacteria live in the small 

intestine. Small intestinal bacterial 

overgrowth is an increase in the number or 

a change in the type of bacteria in the small 

intestine. These bacteria can produce extra 

gas and may also cause diarrhea and weight 

loss. Some researchers believe that small 

intestinal bacterial overgrowth may lead to 

IBS, and some studies have shown antibiotics 

to be effective in treating IBS. However, 

more research is needed to show a link 

between small intestinal bacterial overgrowth 

and IBS.

Body Chemicals

People with IBS have altered levels of 

neurotransmitters—chemicals in the 

body that transmit nerve signals—and GI 

hormones, though the role these chemicals 

play in developing IBS is unclear. Younger 

women with IBS often have more symptoms 

during their menstrual periods. Postmenopausal women have fewer symptoms 

compared with women who are still 

menstruating. These findings suggest that 

reproductive hormones can worsen IBS 

problems.

Genetics

Whether IBS has a genetic cause, meaning 

it runs in families, is unclear. Studies have 

shown IBS is more common in people with 

family members who have a history of GI 

problems. However, the cause could be 

environmental or the result of heightened 

awareness of GI symptoms.

Food Sensitivity

Many people with IBS report that symptoms 

are triggered by foods rich in carbohydrates, 

spicy or fatty foods, coffee, and alcohol. 

However, people with food sensitivity 

typically do not have clinical signs of food 

allergy. Researchers have proposed that 

symptoms may result from poor absorption 

of sugars or bile acids, which help break 

down fats and get rid of wastes in the body.
5 Irritable Bowel Syndrome

How is IBS diagnosed?

To diagnose IBS, a health care provider will 

conduct a physical exam and take a complete 

medical history. The medical history will 

include questions about symptoms, family 

history of GI disorders, recent infections, 

medications, and stressful events related to 

the onset of symptoms. An IBS diagnosis 

requires that symptoms started at least 

6 months prior and occurred at least three 

times a month for the previous 3 months. 

Further testing is not usually needed, though 

the health care provider may perform a 

blood test to screen for other problems. 

Additional diagnostic tests may be needed 

based on the results of the screening blood 

test and for people who also have signs such 

as

•	 fever

•	 rectal bleeding

•	 weight loss

•	 anemia—too few red blood cells in the 

body, which prevents the body from 

getting enough oxygen

•	 family history of colon cancer

•	 family history of irritable bowel 

disease—long-lasting disorders that 

cause irritation and ulcers, or sores, in 

the GI tract

•	 family history of celiac disease—an 

abnormal immune reaction to gluten, a 

protein found in wheat, rye, and barley, 

that damages the lining of the small 

intestine and prevents absorption of 

nutrients

Additional diagnostic tests may include 

a stool test, lower GI series, and flexible 

sigmoidoscopy or colonoscopy. Colonoscopy 

may also be recommended for people who 

are older than age 50 to screen for colon 

cancer.

A stool test is the analysis of a sample of 

stool. The health care provider will give the 

person a container for catching and storing 

the stool. The sample is returned to the 

health care provider or a commercial facility 

and sent to a lab for analysis. The health 

care provider may also do a rectal exam, 

sometimes during the physical exam, to 

check for blood in the stool. Stool tests can 

show the presence of parasites or blood.

A lower GI series is an x ray that is used 

to look at the large intestine. The test is 

performed at a hospital or an outpatient 

center by an x-ray technician, and the 

images are interpreted by a radiologist—a 

doctor who specializes in medical imaging. 

Anesthesia is not needed. The health 

care provider may give written bowel prep 

instructions to follow at home before the 

test. The person may be asked to follow a 

clear liquid diet for 1 to 3 days before the 

procedure. A laxative or an enema may be 

used before the test. A laxative is medication 

that loosens stool and increases bowel 

movements. An enema involves flushing 

water or laxative into the anus using a special 

squirt bottle.
6 Irritable Bowel Syndrome

For the test, the person will lie on a table 

while the radiologist inserts a flexible tube 

into the person’s anus. The large intestine 

is filled with barium, making signs of 

underlying problems show up more clearly 

on x rays.

For several days, traces of barium in the 

large intestine cause stools to be white or 

light colored. Enemas and frequent bowel 

movements may cause anal soreness. A 

health care provider will provide specific 

instructions about eating and drinking after 

the test.

Flexible sigmoidoscopy and colonoscopy

are similar, although colonoscopy is used 

to view the rectum and entire colon, while 

flexible sigmoidoscopy is used to view just 

the rectum and lower colon. These tests 

are performed at a hospital or an outpatient 

center by a gastroenterologist—a doctor 

who specializes in digestive diseases. Before 

either test, a health care provider will give 

written bowel prep instructions to follow at 

home. The person may be asked to follow a 

clear liquid diet for 1 to 3 days before either 

test. The night before either test, the person 

may need to take a laxative or one or more 

enemas. One or more enemas may also 

be required about 2 hours before a flexible 

sigmoidoscopy.

In most cases, light anesthesia and possibly 

pain medication help people relax during 

colonoscopy. For either test, the person will 

lie on a table while the gastroenterologist 

inserts a flexible tube into the anus. A small 

camera on the tube sends a video image of 

the intestinal lining to a computer screen. 

The tests can show signs of problems in the 

lower GI tract.

The gastroenterologist may also perform 

a biopsy, a procedure that involves taking 

a piece of intestinal lining for examination 

with a microscope. The person will not feel 

the biopsy. A pathologist—a doctor who 

specializes in diagnosing diseases—examines 

the tissue in a lab.

Cramping or bloating may occur during the 

first hour after either test. Driving is not 

permitted for 24 hours after a colonoscopy to 

allow the sedative time to wear off. Before 

the appointment, a person should make 

plans for a ride home. Full recovery is 

expected by the next day.

How is IBS treated?

Though IBS does not have a cure, 

the symptoms can be treated with a 

combination of

•	 changes in eating, diet, and nutrition

•	 medications

•	 probiotics

•	 therapies for mental health problems
7 Irritable Bowel Syndrome

Eating, Diet, and Nutrition

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, whole-grain breads and cereals, fruits, 

and vegetables, may help.

Certain foods and drinks may cause IBS 

symptoms in some people, such as

•	 foods high in fat

•	 some milk products

•	 drinks with alcohol or caffeine

•	 drinks with large amounts of artificial 

sweeteners, which are used in place of 

sugar

•	 beans, cabbage, and other foods that 

may cause gas

People with IBS may want to limit or avoid 

these foods. Keeping a food diary is a good 

way to track which foods cause symptoms so 

they can be excluded from or reduced in the 

diet.

Dietary fiber may improve constipation 

symptoms in people with IBS, although it 

may not help with reducing pain. Fiber 

softens stool so it moves smoothly through 

the colon. Adults are advised to consume 

21 to 38 grams of fiber a day.3 Fiber may 

cause gas and trigger symptoms in some 

people with IBS. Increasing fiber intake 

slowly, by 2 to 3 grams a day, may help 

reduce the risk of increased gas and bloating.

3Dietary reference intakes: recommended dietary 

allowances and adequate intakes, total water and 

macronutrients. In: Ross AC, Taylor CL, Yaktine 

AL, Del Valle HB, eds. Dietary Reference Intakes 

for Calcium and Vitamin D. Washington, D.C.: The 

National Academies Press; 2011: 1110.

Medications

A health care provider will select 

medications based on a person’s symptoms.

•	 Fiber supplements may be 

recommended to relieve constipation 

when increasing dietary fiber is 

ineffective.

•	 Laxatives may help constipation. 

Laxatives work in different ways, and 

a health care provider can provide 

information about which type is best for 

each person. Read more in Constipation

at www.digestive.niddk.nih.gov.

•	 Loperamide is an antidiarrheal that has 

been found to reduce diarrhea in people 

with IBS, though it does not reduce 

pain, bloating, or other symptoms. 

Loperamide reduces stool frequency 

and improves stool consistency by 

slowing the movement of stool through 

the colon.

•	 Antispasmodics, such as hyoscine, 

cimetropium, and pinaverium, help to 

control colon muscle spasms and reduce 

abdominal pain.

•	 Antidepressants, such as low doses of 

tricyclic antidepressants (TCAs) and 

selective serotonin reuptake inhibitors 

(SSRIs), can help relieve IBS symptoms, 

including abdominal pain. In theory, 

TCAs should be better for people with 

IBS-D and SSRIs should be better for 

people with IBS-C due to the effect 

on colon transit, although this theory 

has not been confirmed in clinical 

studies. TCAs work in people with 

IBS by reducing sensitivity to pain in 

the GI tract as well as normalizing GI 

motility and secretion.
8 Irritable Bowel Syndrome

•	 Lubiprostone (Amitiza) is prescribed 

for people who have IBS-C. The 

medication has been found to improve 

abdominal pain or discomfort, stool 

consistency, straining, and constipation 

severity.

•	 Linaclotide (Linzess) is also prescribed 

for people who have IBS-C. Linzess has 

been found to relieve abdominal pain 

and increase the frequency of bowel 

movements.

The antibiotic rifaximin can reduce 

abdominal bloating by treating small 

intestinal bacterial overgrowth; however, 

scientists are still debating the use of 

antibiotics to treat IBS and more research is 

needed.

Probiotics

Probiotics are live microorganisms, 

usually bacteria, that are similar to 

microorganisms normally found in 

the GI tract. Studies have found that 

when taken in large enough amounts, 

probiotics, specifically Bifidobacteria and 

certain probiotic combinations, improve 

symptoms of IBS. However, more research 

is needed. Probiotics can be found in 

dietary supplements, such as capsules, 

tablets, and powders, and in some foods, 

such as yogurt. A health care provider can 

give information about the right kind and 

amount of probiotics to take to improve 

IBS symptoms. To help ensure coordinated 

and safe care, people should discuss their 

use of complementary and alternative 

medical practices, including their use of 

dietary supplements and probiotics, with 

their health care provider. Read more at 

www.nccam.nih.gov/health/probiotics.

Therapies for Mental Health 

Problems

The following therapies can help improve 

IBS symptoms due to mental health 

problems:

•	 Talk therapy may reduce stress and 

improve IBS symptoms. Two types 

of talk therapy used to treat IBS are 

cognitive behavioral therapy and 

psychodynamic, or interpersonal, 

therapy. Cognitive behavioral therapy 

focuses on a person’s thoughts and 

actions. Psychodynamic therapy focuses 

on how emotions affect IBS symptoms. 

This type of therapy often involves 

relaxation and stress management 

techniques.

•	 Hypnotherapy may help a person relax 

the muscles in the colon.

•	 Mindfulness training teaches people 

to focus their attention on sensations 

occurring at the moment and avoid 

catastrophizing, or worrying about the 

meaning of those sensations.
9 Irritable Bowel Syndrome

What other conditions are 

associated with IBS?

People with IBS often suffer from other 

GI and non-GI conditions. GI conditions 

such as gastroesophageal reflux disease 

(GERD) and dyspepsia are more common 

in people with IBS than the general 

population. GERD is a condition in 

which stomach contents flow back up into 

the esophagus—the organ that connects 

the mouth to the stomach—because the 

muscle between the esophagus and the 

stomach is weak or relaxes when it should 

not. Dyspepsia, or indigestion, is upper 

abdominal discomfort that often occurs 

after eating. Dyspepsia may be accompanied 

by fullness, bloating, nausea, or other GI 

symptoms. Read more in Gastroesophageal 

Reflux (GER) and Gastroesophageal Reflux 

Disease (GERD) in Adults and Indigestion at 

www.digestive.niddk.nih.gov. 

Non-GI conditions often found in people 

with IBS include

•	 chronic fatigue syndrome—a disorder 

that causes extreme fatigue, which is 

tiredness that lasts a long time and 

limits a person’s ability to do ordinary 

daily activities

•	 chronic pelvic pain

•	 temporomandibular joint disorders—

problems or symptoms of the chewing 

muscles and joints that connect the 

lower jaw to the skull

•	 depression

•	 anxiety

•	 somatoform disorders—chronic pain 

or other symptoms with no physical 

cause that are thought to be due to 

psychological problems

How does stress affect IBS?

Stress can stimulate colon spasms in people 

with IBS. The colon has many nerves that 

connect it to the brain. These nerves control 

the normal contractions of the colon and 

cause abdominal discomfort at stressful 

times. 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. IBS 

symptoms can also increase a person’s stress 

level. Some options for managing stress 

include

•	 participating in stress reduction and 

relaxation therapies such as meditation

•	 getting counseling and support

•	 taking part in regular exercise such as 

walking or yoga

•	 minimizing stressful life situations as 

much as possible

•	 getting enough sleep
10 Irritable Bowel Syndrome

Points to Remember

•	 Irritable bowel syndrome (IBS) is 

a functional gastrointestinal (GI) 

disorder, meaning symptoms are 

caused by changes in how the GI tract 

works. People with a functional GI 

disorder have frequent symptoms; 

however, the GI tract does not 

become damaged.

•	 IBS is a group of symptoms that occur 

together, not a disease.

•	 Studies estimate IBS affects 3 to 

20 percent of the adult population, 

with most studies ranging from 

10 to 15 percent. However, only 5 to 

7 percent of the adult population has 

been diagnosed with the condition.

•	 The most common symptoms of IBS 

are abdominal pain or discomfort, 

often reported as cramping, along 

with changes in bowel habits. Other 

symptoms of IBS may include 

– diarrhea

– constipation

– feeling that a bowel movement is 

incomplete

– passing mucus

– abdominal bloating

•	 The causes of IBS are not well 

understood. Researchers believe a 

combination of physical and mental 

health problems can lead to IBS.

•	 To diagnose IBS, a health care 

provider will conduct a physical 

exam and take a complete medical 

history. The medical history will 

include questions about symptoms, 

family history of GI disorders, 

recent infections, medications, and 

stressful events related to the onset of 

symptoms.

•	 Though IBS does not have a cure, 

the symptoms can be treated with a 

combination of 

– changes in eating, diet, and 

nutrition

– medications

– probiotics

– therapies for mental health 

problems
11 Irritable Bowel Syndrome

Hope through Research

The National Institute of Diabetes and 

Digestive and Kidney Diseases’ (NIDDK’s) 

Division of Digestive Diseases and Nutrition 

conducts and supports basic and clinical 

research into many digestive disorders. 

Clinical trials are research studies involving 

people. Clinical trials look at safe and 

effective new ways to prevent, detect, or 

treat disease. Researchers also use clinical 

trials to look at other aspects of care, such 

as improving the quality of life for people 

with chronic illnesses. To learn more about 

clinical trials, why they matter, and how to 

participate, visit the NIH Clinical Research 

Trials and You website at www.nih.gov/health/

clinicaltrials. For information about current 

studies, visit www.ClinicalTrials.gov.

For More Information

American Neurogastroenterology and 

Motility Society

45685 Harmony Lane 

Belleville, MI 48111 

Phone: 734–699–1130 

Fax: 734–699–1136 

Email: admin@motilitysociety.org

Internet: www.motilitysociety.org 

International Foundation for Functional 

Gastrointestinal Disorders

700 West Virginia Street, Suite 201

Milwaukee, WI 53204

Phone: 1–888–964–2001 or 414–964–1799

Fax: 414–964–7176

Email: iffgd@iffgd.org

Internet: www.iffgd.org

Rome Foundation, Inc.

P.O. Box 6524 

Raleigh, NC 27628 

Phone: 919–539–3051 

Fax: 919–900–7646 

Email: mpickard@theromefoundation.org 

Internet: www.romecriteria.org 

Acknowledgments

Publications produced by the Clearinghouse 

are carefully reviewed by both NIDDK 

scientists and outside experts. This 

publication was reviewed by William E. 

Whitehead, Ph.D., University of North 

Carolina Center for Functional GI and 

Motility Disorders.

You may also find additional information about this 

topic by visiting MedlinePlus at www.medlineplus.gov.

This publication may contain information about 

medications and, when taken as prescribed, the 

conditions they treat. 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 tollfree at 1–888–INFO–FDA (1–888–463–6332) or visit 

www.fda.gov. Consult your health care provider for 

more information.

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If a product is not mentioned, the omission does not 

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NIH Publication No. 13–693

September 2013

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