Southern Cross Medical Library

Southern Cross Medical Library

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

About IBS

IBS appears to be a relatively 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 about 7% of New Zealanders.

IBS is not a disease as such. It is a group of symptoms that occur together and which require long-term management.

IBS is unpleasant and bothersome but does not result in lasting damage to the intestinal tissues or increase the risk of bowel cancer. It is important, however, to get a proper diagnosis so that more serious illnesses (such as bowel cancer or inflammatory bowel diseases) that cause similar symptoms can be ruled out.

Diagram of gastrointestinal tract

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 IBS.


It is not known what causes IBS. What is known is that the condition involves disruption in the normal movement of the muscles in the outer wall of the intestine.

Normally, 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
  • Bacterial overgrowth: IBS has been associated with a surplus of bacteria in the intestines
  • Changes in the intestinal microbiome: these are the ‘friendly’ bacteria that live in the gut, which are important for digestion and health in general. The microbiome in people with IBS appears to differ from that in healthy people.
  • Food intolerances: many people with IBS report that some foods and beverages can cause symptoms.

Signs and symptoms

IBS 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.

In many people, the symptoms of IBS come and go.

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 IBS 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 IBS. 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, a person must have had recurrent abdominal pain on average at least one day per week during the previous three months that is associated with two or more of the following:

  • The pain is increased or unchanged after a bowel movement
  • A change in frequency of bowel movements
  • A change in stool form or appearance.

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.

Tests for lactose tolerance (caused by a lack of lactase, which is an enzyme required to digest the carbohydrate lactose in dairy products) may be performed because the symptoms of lactose intolerance - mainly abdominal pain, gas, and diarrhoea - are similar to those caused by IBS.

A breath test may be done to determine if bacterial overgrowth in the intestine might be responsible for IBS symptoms. Bacterial overgrowth is common among people who have had bowel surgery.

To avoid unnecessary tests or operations, your doctor may refer you to a specialist (gastroenterologist) for additional diagnosis. Stool tests and blood tests for anaemia and signs of inflammation may be ordered to exclude other more serious diseases of the intestines, such as intestinal infections, coeliac disease (gluten intolerance), bowel cancer, ulcerative colitis, and Crohn’s disease.

Sigmoidoscopy (the lower portion of the intestine is examined with a flexible camera) and colonoscopy (the entire length of the intestine is examined with a flexible camera) may also be required to exclude more serious diseases.


There is no cure for IBS. 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.
  • Anti-diarrhoea medications: Doctors may prescribe bile acid binders. Medicines you can get from your pharmacy without prescription, like loperamide, may help control diarrhoea.
  • Antidepressants: If symptoms include pain or depression a doctor may recommend medications that relieve depression.
  • Fibre supplements: Such as psyllium can be used to treat constipation and possibly some of the other symptoms of IBS.
  • Laxatives: These may be effective for treating constipation if fibre supplements do not help to relieve symptoms.
  • Peppermint oil: A natural anti-spasmodic, 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 of the intestinal microbiome) may help with digestion.


Dietary changes can also help control symptoms of IBS. Eating at about the same time each day should help regulate bowel function.

Foods that typically make IBS symptoms worse should be limited or avoided. Alcohol, chocolate, caffeinated beverages are potential culprits as are certain types of carbohydrate known as FODMAPs. FODMAPS include fructose (which is found in fruits) and lactose (which is found in milk and dairy products).

If diarrhoea is a problem, eating smaller meals more often, or eating smaller portions, may lessen symptoms.

If constipation is a problem, eating larger amounts of high-fibre foods may promote the movement of food through the intestines. High-fibre foods include whole grain breads, seeds, nuts, cereals, fruits, and vegetables. However, some fruits and vegetables such as beans, cabbage, cauliflower, and broccoli are best avoided if gas and bloating are primary symptoms.

Some people may find a gluten free diet (ie: without wheat, rye and barley) may be beneficial for their symptoms.

Keeping a food diary may help determine what effects different foods have for you.


Lehrer, J.K. (2019). Irritable bowel syndrome (Web page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. [Accessed: 09/09/20]
Mayo Clinic (2018). Irritable bowel syndrome (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. [Accessed: 09/09/20]
O’Toole, M.T. (Ed.) (2017). Irritable Bowel Syndrome. Mosby’s Dictionary of Medicine, Nursing & Health Professions (10th ed.). St Louis MI: Elsevier.
Sperber, A.D., et al. (2017). The global prevalence of IBS in adults remains elusive due to the heterogeneity of studies: a Rome Foundation working team literature review. Gut. 2017;66(6):1075–1082.

Last reviewed: September 2020

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The purpose of the Southern Cross Medical Library is to provide information of a general nature to help you better understand certain medical conditions. Always seek specific medical advice for treatment appropriate to you. This information is not intended to relate specifically to insurance or healthcare services provided by Southern Cross.