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Southern Cross Medical Library

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Irritable bowel syndrome (IBS)

Irritable bowel syndrome (IBS) is a common disorder of the small and large intestine (bowel). Its cause is unknown, while symptoms include bloating, abdominal pain and alternating constipation and diarrhoea.  There is no cure for irritable bowel syndrome so the aim of treatment is to control symptoms. In many cases, this can be achieved by managing diet, lifestyle and stress.

General Information

Strictly speaking, irritable bowel syndrome is not a disease – it is a group of symptoms that occur together.  The condition is unpleasant and bothersome but does not result in lasting damage to the intestinal tissues or increase the risk of intestinal cancer. It is important, however, to get a proper diagnosis so that other illnesses that cause similar symptoms can be ruled out.
It is a common condition but exactly how common is not known due to difficulty in diagnosing the disorder and because few people (only 1 in 20) go to see a doctor because of the symptoms. However, it has been estimated that IBS affects 15-20% of people in the US and Europe. A similar rate of occurrence has been found in New Zealand.
The condition tends to appear when people are young or middle-aged (before age 45 years), rather than later in life, and affects twice as many women as men.  Functional bowel syndrome, nervous colon, spastic colon, and irritable colon are other names for the condition.


It is not known what causes irritable bowel syndrome. What is known is that the condition involves disruption in the normal movement of the muscles in the outer wall of the intestine.  Intestinal wall muscles relax and contract (tighten) automatically to push food and waste through the intestine so that water and nutrients can be absorbed by the body.
In IBS, the muscles may relax and contract more rapidly than normal so that less water is absorbed, which results in soft and watery stools, i.e. diarrhoea. Or the muscles may contract and relax more slowly than normal so that too much water is absorbed, which results in hard stools, i.e. constipation. The muscles may also contract suddenly and very strongly, i.e. spasm, which causes painful abdominal cramps and gas to become trapped in the intestine causing bloating.

It is not known what causes intestinal muscles to stop working properly in IBS. One suggestion is that communication signals between the brain and the intestine are disrupted and this results in abnormal function of the intestinal muscles.  Potential causes of IBS include:

  • Hypersensitivity: some people with IBS have a lower pain threshold to bloating and cramping in their intestines.
  • Infection: bacterial gastroenteritis may trigger IBS in some people.
  • Stress: stressful events, such as work or marriage difficulties, or the death of someone close, may also trigger symptoms of IBS. Psychological stress can be expressed through physical symptoms. Stress can also worsen IBS.
  • Body chemicals: levels of neurotransmitters (chemicals that transmit nerve signals) and digestive tract hormones are altered in some people with IBS. Reproductive hormones appear to worsen symptoms.
  • Food sensitivity: many people with IBS report that some foods and beverages can cause symptoms.

Signs and symptoms

Irritable bowel syndrome affects people in different ways but pain and discomfort are symptoms that occur in all people with the condition. Bloating is also a common symptom. Some people may experience diarrhoea but not constipation, some people may experience constipation but not diarrhoea, and other people may experience bouts of both.
Symptoms not related to the intestine, such as painful periods, back pain, headaches and general tiredness may also be present in people with IBS. These symptoms may be due to stress or people with IBS worrying more about their health.
Symptoms similar to irritable bowel syndrome may be a sign of something more serious so it is important to see your doctor for a full diagnosis.


There is no test that can confirm a diagnosis of irritable bowel syndrome. A diagnosis is made by a doctor asking questions about symptoms and other health problems, and ruling out other illnesses. For a doctor to make a diagnosis of IBS one of the following must also be true:

  • You have pain or discomfort that is relieved by going to the toilet
  • You have pain or discomfort that is accompanied by a change in frequency of bowel movements or in stool form (appearance), i.e. harder or softer.

And two of the following must be true:

  • You experience a change in how you pass stools, eg: you feel an urgency to go to the toilet, strain to pass stools, or feel as if you have not completely emptied your bowels
  • You have bloating or hardness in your abdomen
  • Your symptoms tend to feel worse after you eat
  • Your stools may have mucous in them.
Another factor in making a diagnosis of IBS is that there has been a change in symptom frequency and duration – typically that symptoms started at least six months before seeing a doctor and have occurred at least three days per month for the previous three months.
Your doctor may also ask whether you get pain in just one spot in your abdomen or if it moves around. In IBS, the pain does not usually stay in the same place.  You might also have other general symptoms, such as backaches and feeling tired, which can help confirm the diagnosis of IBS.
To avoid unnecessary tests or operations, your doctor may refer you to a specialist for additional diagnosis.  Blood tests for anaemia and signs of inflammation may be ordered to exclude other diseases of the intestines, such as ulcerative colitis and Crohn’s disease.


There is no cure for irritable bowel syndrome. Medications are used to help to control symptoms but are recommended only if they are really needed. There are things that people with IBS can do themselves that can help, such as finding ways to better cope with stress and anxiety, and learning more about the condition. Dietary changes may also be beneficial in controlling symptoms.


  • Anti-spasmodic drugs: relax the muscles in the wall of your intestines to stop painful spasms. They include mebeverine (Colofac), and hyoscine (Buscopan, Gastrosoothe).
  • Loperamide (Diamide Relief): is sometimes used to treat diarrhoea in people with IBS.
  • Antidepressants: although normally used to treat depression, these medications may have benefits in some people with IBS. Examples include, amitriptyline (Amitrip), clomipramine (Apo-Clomipramine), and doxepin (Anten).
  • Fibre supplements: such as sterculia (Normacol), can be used to treat constipation and possibly some of the other symptoms of IBS.
  • Peppermint oil: which can relax the muscles in your intestine, is sometimes used to treat symptoms of IBS.
  • Probiotics: products, such as probiotic yoghurts, soy drinks, and tablets and capsules (which contain live ‘friendly’ bacteria similar to those that live in your bowels) can help with digestion.

Alternative therapies

Some people report positive outcomes from alternative therapies. Examples include talking therapies that help people deal with stress and feelings, hypnotherapy and acupuncture.


Dietary changes can also help control symptoms of irritable bowel syndrome. Large meals can cause cramping and diarrhoea – eating smaller meals more often, or eating smaller portions, may lessen symptoms. Eating meals low in fat and high in carbohydrates, such as pasta, rice, whole-grain breads and cereals, fruits, and vegetables, may also help.

Support and further information

For further support and information:  Crohn’s & Colitis New Zealand Charitable Trust
Phone: 0800 ASK IBD (0800 275 423)
Irritable Bowel Information & Support Association of Australia Inc. (IBIS)
Phone: +61 (07) 3376-2496


Barbezat, G., Poulton, R., Milne, B., Fawcett, J.P., Talley, N. (2002). Prevalence and correlates for irritable bowel symptoms in a New Zealand birth cohort. New Zealand Medical Journal 115(1164):U220.
Marks, J.W. (2012). Irritable Bowel Syndrome (IBS). New York: WebMD LLC.
National Digestive Diseases Information Clearinghouse (2012). Irritable Bowel Syndrome. Bethesda: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health of the U.S. Department of Health and Human Services.
O’Toole, M.T. (Ed.) (2013) Irritable Bowel Syndrome. Mosby’s Dictionary of Medicine, Nursing & Health Professions (9th ed.) St Louis: Elsevier Mosby.
Wyeth, J.W. (2011). Functional gastrointestinal disorders in New Zealand. Journal of Gastroenterology and Hepatology 26 (Suppl. 3):15-18.
Created: June 2013
Go to our Medical Library Index Page to find information on other medical conditions.