Irritable bowel syndrome: causes, symptoms and treatment

by | Gastrointestinal Health, Symptoms

irritable bowel syndrome (IBS)

Irritable bowel syndrome (IBS) is a common, long-term disorder that affects the large intestine (bowel or colon). It can cause abdominal pain, cramps, bloating and bouts of diarrhoea or constipation. IBS affects around 15 per cent of Australians and is more common in women than in men.

IBS tends to appear in people aged in their twenties, although it may develop in younger and older people. It is unusual for IBS to first appear in someone aged over 40 years.

IBS does not cause permanent damage to the digestive tract or lead to serious disease, such as cancer. While there is currently no cure, there are treatments available that can relieve the symptoms of IBS.

What are the symptoms of IBS?

The symptoms of IBS may vary from person to person. Symptoms tend to come and go over time, and often last for several days or weeks. There may be times when symptoms are worse than others.

Common symptoms of IBS include:

  • Abdominal pain and cramps.
  • Abdominal bloating.
  • Diarrhoea and/or constipation (sometimes these may alternate).
  • Excessive flatulence (wind).
  • Mucus in the stool.
  • Urgent need to go to the toilet.
  • Feeling of not having completely emptied the bowels after going to the toilet.

The symptoms of IBS are often relieved by a bowel movement (passing stool).

What symptoms are not caused by IBS?

If a person notices bleeding from the back passage, blood in the stool, fever, weight loss or severe diarrhoea at night, it is important to see a doctor for further assessment. These symptoms are not caused by IBS and may indicate a more serious condition.

A person should also see a doctor if their symptoms get progressively worse, stools are pale, bulky, very offensive smelling and difficult to flush away (this may indicate a problem with absorbing fat), or if they are concerned about their symptoms.

What causes IBS?

The exact cause of IBS is unknown, but experts think that several factors may be involved. These include:

  • Problems with digestion: the muscles of the intestines work to squeeze food through the digestive system. In people with IBS, this process may not be working properly, so that food moves through the digestive system too slowly or too quickly. If it moves too slowly it can lead to constipation; if it moves too quickly it may cause diarrhoea.
  • Overactivity of the nerves in the intestines: if the nerves in the digestive system are oversensitive, they may cause people to feel more pain. This oversensitivity may cause the crampy abdominal pain associated with IBS.
  • Genetic and early life factors: close relatives of a person with IBS may be more likely to develop IBS themselves; some early childhood experiences (e.g. poor nutrition) may also be involved in the development of IBS.

IBS is not caused by a blood or biochemical disorder.

What triggers IBS?

Triggers (things that bring on an episode of IBS) vary from person to person. The most common triggers include:

  • Certain foods and drinks (these vary widely and include fizzy drinks, alcohol, drinks containing caffeine, chocolate, beans, cabbage, dairy products, spices, fruits, fatty or fried food).
  • Eating too quickly or too much.
  • Stress and anxiety.
  • Hormonal changes (e.g. some women have IBS just before, or during, their menstrual period).
  • Gastrointestinal infections: some people develop IBS after a gastrointestinal infection.

It is important that people try to identify their own triggers so that they can avoid or minimise IBS symptoms.

How is IBS diagnosed?

The diagnosis of IBS can be challenging, because the symptoms are also seen in other digestive conditions. There is no one test that can show whether a person has IBS. A doctor will usually base the diagnosis on a person’s symptoms and the elimination of other causes. Sometimes investigations such as blood tests may be done to rule out other conditions.

To help the process of diagnosis, experts have developed a set of criteria to help determine if a person has IBS.

One example is the Rome criteria – this definition says that a person with IBS will have had abdominal pain and discomfort that lasts for at least 3 days a month in the last 3 months, plus 2 or more of the following:

  • Improvement of symptoms with a bowel movement.
  • Altered frequency of bowel movements (e.g. going to the toilet more or less often).
  • Altered consistency of stool (e.g. softer, harder).


The main treatment for irritable bowel syndrome is making dietary and lifestyle modifications, including stress management, getting enough sleep and exercise. It can also be helpful to keep a diary of events surrounding each episode to help identify things that may trigger IBS symptoms or make them worse, such as trigger foods.

There are also treatments available that can relieve the symptoms. Symptom-specific treatment for IBS includes products to alleviate diarrhoea, constipation and pain.

Diet for IBS

Developing a routine eating pattern that involves regular small meals is a good place to start. Make sure you eat a good variety of foods, and avoid excessive amounts of coffee or alcohol.

Avoiding any foods that you know aggravate your IBS symptoms is also a good idea. Some common foods that can cause problems for people with IBS include: beans, broccoli, cabbage, cauliflower, fats, spices, alcohol, caffeine and carbonated drinks.

If you are not sure which foods seem to trigger your symptoms, record what you eat and your symptoms for a week or 2, and discuss the results with your doctor. Don’t eliminate any major food groups from your diet without first discussing your dietary needs with your doctor or a dietitian.

Low-FODMAP diet

Foods that are high in FODMAPs often cause problems for people with IBS. FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) are a collection of types of carbohydrate, specifically sugars and sweeteners, that can be difficult to digest. Examples of these foods include:

  • fruits such as apples, apricots, watermelon, mangoes and pears;
  • vegetables such as garlic, lentils, mushrooms, onions, beans and cabbage;
  • some dairy products (e.g. milk, yoghurt, ice cream);
  • foods containing wheat or rye;
  • honey;
  • foods containing high-fructose corn syrup; and
  • certain artificial sweeteners.

Many people find that some of these foods aggravate their symptoms but not others. Your doctor may recommend seeing a dietitian to help determine whether a low-FODMAP diet may be of benefit.


Stool bulking with fibre (dietary or supplemental) may help relieve symptoms of constipation. However, fibre should be introduced gradually to minimise the side effects of abdominal gas and bloating.

Dietary changes that increase your fibre intake include eating wholemeal or wholegrain breads and cereals, and plenty of fresh fruits and vegetables.

If up to 30 grams of dietary fibre per day is not effective for relieving constipation, supplemental fibre, such as psyllium may be an option.

You should also increase your fluid intake and take regular exercise.


Foods (such as yoghurt) and supplements that contain probiotics – so-called ‘good’ bacteria that are normally found in your bowel – may help with some symptoms of IBS, including diarrhoea, pain and bloating.

Medicines for IBS

Medicines are available to treat the different symptoms of IBS, so your doctor will recommend treatment based on whether you have diarrhoea-predominant IBS (IBS-D) or constipation-predominant IBS (IBS-C).

Medicines for diarrhoea

Anti-diarrhoeal medicines are effective when taken ‘as-needed’ on an intermittent basis.

Anti-diarrhoeal medicines include:

  • loperamide (brand names include Imodium, Gastro-Stop, Stop-It); and
  • atropine plus diphenoxylate (e.g. Lomotil, Lofenoxal).

Side effects will depend on the type of medicine you take.

Medicines and supplements for constipation

If constipation is severe, increased fibre may be ineffective and may worsen abdominal pain and bloating. In this case your doctor may recommend laxatives.

Stimulant laxatives such as senna should generally be avoided, as should prolonged use of any laxative.

Some of the over-the-counter products available to relieve constipation include:

  • psyllium (e.g. Metamucil);
  • macrogol 3350 (e.g. Movicol, OsmoLax);
  • frangula plus sterculia (Normacol Plus);
  • lactulose (e.g. Actilax, Dulose, Duphalac);
  • sorbitol (e.g. Sorbilax, Sorbisol);
  • paraffin liquid (e.g. Agarol, Parachoc); and
  • docusate (e.g. Coloxyl).

Side effects

Some laxatives are not suitable for certain people. People with irritable bowel syndrome tend to find the side effects of lactulose and sorbitol (such as wind, bloating, cramping, diarrhoea) difficult to manage. Check with your doctor about the most appropriate type of laxative for you.

Medicines for pain and bloating

Medicines that relieve abdominal cramping should be used ‘as-needed’, rather than on a regular basis. These medicines may also be used preventively when pain is predicted, such as after large meals.

Prescription and over-the-counter products that help alleviate the pain associated with IBS include:

  • peppermint oil (brand name Mintec);
  • hyoscine butylbromide (e.g. Buscopan, Setacol);
  • hyoscyamine plus hyoscine hydrobromide plus atropine (brand name Donnatab); and
  • mebeverine (e.g. Colofac, Colese).

Some antidepressant medicines including tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs), when taken in low doses, may be beneficial in reducing pain in people with IBS. In these situations the antidepressant medicines are being used for their pain-relieving properties rather than for their effect on mood.

Side effects will depend on the type of medicine you take.

Psychological therapies

Stress, anxiety and depression can trigger symptoms of IBS, so managing these problems can help.

There are several psychological therapies that can be used in the treatment of irritable bowel syndrome.

  • Cognitive behavioural therapy (CBT) is a type of therapy that involves identifying and challenging negative thinking patterns and developing alternative ways of thinking and acting.
  • Hypnotherapy is a technique where a therapist guides you to enter a relaxed state and to relax your abdominal muscles to help relieve pain and bloating.
  • Relaxation therapy or meditation can help relieve stress.
  • Counselling may be an important part of treatment for stress, depression or anxiety and related symptoms.

Getting regular physical activity can also help relieve stress and depression, and help restore normal contractions in your bowel.