The reasons why IBS develops are not clear. It can occur after a bacterial infection or a parasitic infection (giardiasis) of the intestines. This is called postinfectious IBS. There may also be other triggers, including stress.

The intestine is connected to the brain by hormone and nerve signals that go back and forth between the bowel and the brain. These signals affect bowel function and symptoms. The nerves can become more active during stress. This can cause the intestines to be more sensitive and contract more.

IBS can occur at any age. Often, it begins in the teen years or early adulthood. It is twice as common in women as in men.

 It is less likely to begin in people above 50 years of age.

About 10% to 15% of people in the United States have symptoms of IBS. It is the most common intestinal problem that causes people to be referred to a bowel specialist (gastroenterologist).

IBS symptoms vary from person to person, and range from mild to severe. Most people have mild symptoms. You are said to have IBS when symptoms are present for at least 3 days a month for a period of 3 months or more.

The main symptoms include:

• Abdominal pain and cramps
• Gas
• Fullness
• Bloating
• Change in bowel habits. You can have either diarrhea (IBS-D), or constipation (IBS-C).

Pain and other symptoms will often be reduced or go away after a bowel movement. Symptoms may flare up when there is a change in the frequency of your bowel movements.

People with IBS may go back and forth between having constipation and diarrhea or have or mostly have one or the other.

• If you have IBS with diarrhea, you will have frequent, loose, watery stools. You may have an urgent need to have a bowel movement, which may be hard to control.
• If you have IBS with constipation, you will have a hard time passing stool, as well as fewer bowel movements. You may need to strain with a bowel movement and have cramps. Often, only a small amount or no stool at all will pass.

The symptoms may get worse for a few weeks or a month, and then decrease for a while. In other cases, symptoms are present most of the time.

You may also lose your appetite if you have IBS. However, blood in stools and unintentional weight loss are not a part of IBS.

There is no test to diagnose IBS. Most of the time, your health care provider can diagnose IBS based on your symptoms. Eating a lactose-free diet for 2 weeks may help the provider identify lactase deficiency (or lactose intolerance).

The following tests may be done to rule out other problems:

• Blood tests to see if you have celiac disease or a low blood count (anemia)
• Stool exam for occult blood (blood that is not visible)
• Stool cultures to check for an infection
• Microscopic exam of a stool sample for parasites
• Stool exam for a substance called fecal calprotectin

Your provider may recommend a colonoscopy. During this test, a flexible tube is inserted through the anus to examine the colon. You may need this test if:

• Symptoms began later in life (age 50 or over)
• You have symptoms such as weight loss or bloody stools
• You have abnormal blood tests (such as a low blood count)

Other disorders that can cause similar symptoms include:

• Celiac disease
• Colon cancer (cancer rarely causes typical IBS symptoms, unless symptoms such as weight loss, blood in the stools, or abnormal blood tests are also present)
• Crohn disease or ulcerative colitis

The goal of treatment is to relieve symptoms.

In some cases of IBS, lifestyle changes can help. For example, regular exercise and improved sleep habits may reduce anxiety and help relieve bowel symptoms.

Dietary changes can be helpful. However, no specific diet can be recommended for IBS because the condition differs from one person to another.

The following changes may help:

• Avoiding foods and drinks that stimulate the intestines (such as caffeine-containing drinks, tea, or colas)
• Eating smaller meals
• Increasing fiber in the diet (this may improve constipation or diarrhea, but make bloating worse)

Talk with your provider before taking over-the-counter medicines.

No one medicine works for everyone. Some that your provider may suggest include:

• Anticholinergic medicines (dicyclomine, propantheline, belladonna, and hyoscyamine) taken about a half-hour before eating to control intestinal muscle spasms
• Loperamide to treat IBS-D
• Alosetron (Lotronex) for IBS-D
• Eluxadoline (Viberzi) for IBS-D
• Probiotics
• Low doses of tricyclic antidepressants to help relieve intestinal pain
• Lubiprostone (Amitiza) for IBS-C
• Bisacodyl to treat IBS-C
• Rifaximin, an antibiotic
• Linaclotide (Linzess) for IBS-C

Psychological therapy or medicines for anxiety or depression may help with the problem.

IBS may be a life-long condition. For some people, symptoms are disabling and interfere with work, travel, and social activities.

Symptoms often get better with treatment.

IBS does not cause permanent harm to the intestines. Also, it does not lead to a serious disease, such as cancer.

Contact your provider if you have symptoms of IBS or if you notice changes in your bowel habits that do not go away.

IBS; Irritable bowel; Spastic colon; Irritable colon; Mucous colitis; Spastic colitis; Abdominal pain - IBS; Diarrhea - IBS; Constipation - IBS; IBS-C; IBS-D

Aronson JK. Laxatives. In: Aronson JK, ed. Meyler's Side Effects of Drugs. 16th ed. Waltham, MA: Elsevier; 2016:488-494.

Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clin Epidemiol. 2014;6:71-80. PMID: 24523597 pubmed.ncbi.nlm.nih.gov/24523597/.

Charles MB. Common clinical manifestations of gastrointestinal disease: abdominal pain. In: Wing EJ, Schiffman FJ, eds. Cecil Essentials of Medicine. 10th ed. Philadelphia, PA: Elsevier; 2022:chap 31.

Ferri FF. Irritable bowel syndrome. In: Ferri FF, ed. Ferri's Clinical Advisor 2023. Philadelphia, PA: Elsevier; 2023:875-877.

Ford AC, Talley NJ. Irritable bowel syndrome. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology/Diagnosis/Management. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 122.

Mayer EA. Functional gastrointestinal disorders: irritable bowel syndrome, dyspepsia, chest pain of presumed esophageal origin, and heartburn. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 128.

Updated by: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.