Irritable bowel syndrome

Contributed by Professor Greg Rubin, GP and professor of general practice and primary care, Durham University.

Section 1 Aetiology and epidemiology
Irritable bowel syndrome (IBS) is a functional gastroenterological disorder of the colon in which abdominal pain or discomfort is associated with change in bowel habit and bloating or distension.

IBS is the most common GI disorder seen in primary care.

Despite this, only about 25 per cent of patients with IBS seek medical attention.

The British Society of Gastroenterology has acknowledged the significance of the problem by the publication of comprehensive guidelines for its diagnosis and management.1

Also relevant to GPs are the Primary Care Society for Gastroenterology (PCSG) guidelines for the primary care management of IBS.2

Distended colon due to constipation in IBS, seen on barium X-ray

The size of the problem
About 12 per cent of the UK population experiences IBS symptoms in any 12-month period. The precise incidence of the condition is not accurately known, but has been estimated at almost 1 per cent per year.

In general, women are twice as likely to have IBS as men, although men are more likely to present with certain specific symptoms, notably frequent and loose stools.

IBS patients consult frequently with GI complaints. They also consult more frequently with non-GI complaints and are more prone to problems such as lethargy and low back pain.

It has been calculated that each consulting IBS patient costs the NHS £90 per year. In the UK, given the incidence of new cases, the overall number of consultations probably reaches 240,000 per year. This translates into an annual cost to the NHS of about £22 million.


  • Key symptoms are pain or discomfort, altered bowel habit and abdominal bloating.
  • Associated non-colonic problems include upper GI symptoms, urinary and gynaecological problems, back pain, lethargy and sometimes migraine, asthma and depression.
  • Older patients with new symptoms and any patients with alarm symptoms need referral.
  • Patients with predominant constipation are most likely to benefit from a high-fibre diet.
  • Dietary manipulation is controversial but some patients report symptoms are strongly related to certain foods.

Section 2 Contributory factors
Most IBS patients managed in primary care do not have serious psychological morbidity. However, referred patients display a higher than normal incidence of psychological symptoms and psychiatric disease.

The role of stress
Studies have shown that, in more than 50 per cent of referred patients, the onset of symptoms is associated with a stressful life event, such as work-related problems, bereavement, a surgical operation or relationship difficulties.3

The pain of IBS appears to be due to visceral hypersensitivity. IBS patients exhibit decreased pain thresholds in response to balloon distension of the gut.

It is probable that the central processing of visceral afferent stimuli is involved.

Significance of infection
Persistent bowel dysfunction is seen in 25 per cent of patients following campylobacter, shigella and salmonella gastro-enteritis.4

Previously infected patients are more sensitive to rectal distension, and rectal biopsies indicate microscopic structural abnormalities.

In one study, which looked at 584,000 patients, the occurrence of bacterial gastroenteritis was the strongest predictor of new-onset IBS in the 12 months after enteric infection, with a relative risk of 11.9.5

Although many patients believe that some types of food exacerbate their IBS symptoms, evidence that the gut is sensitive to certain food types is limited.

However, studies that have incorporated dietary restrictions followed by sequential introduction of single foods have reported food intolerance in between one and two thirds of IBS patients.

The most common food intolerances in the UK involve wheat, dairy products and coffee.

A lactose-free diet may improve IBS symptoms in some patients, although even lactose malabsorbers do not experience symptoms if their intake is less than 0.25 litres of milk per day.

Section 3 Diagnosis
A careful and detailed history is important, and is often developed over several consultations. This history should identify any relevant psychological factors, family history and personal circumstances.

A dietary history is also useful as this will help identify any unusual dietary habits or triggering medications. For example, both excess and lack of dietary fibre may provoke symptoms in susceptible individuals.

The same is true of excesses of poorly absorbed sugars such as fructose.

Drug history
Several drugs can affect the likelihood of patients experiencing diarrhoea or constipation. Diarrhoea-predominant effects have been reported with ACE inhibitors, beta-blockers, antibiotics, chemotherapeutic agents, proton-pump inhibitors and NSAIDs.

In contrast, constipation-predominant effects have been seen with opiate analgesics, calcium-channel blockers and tricyclic antidepressants.

Further assessment
Most IBS patients are diagnosed in primary care, based on the identification of symptoms consistent with the syndrome and the exclusion of organic diseases that have similar clinical presentations.

Criteria for diagnosis
NICE have recently made recommendations on the diagnosis and management of IBS.6 They advise that IBS should be considered if the patient reports at least six months of abdominal pain or discomfort, bloating or a change in bowel habit.

A positive diagnosis can be made if abdominal pain or discomfort is relieved by defecation or associated with altered bowel frequency or form. The pain should be accompanied by at least two of the following:

  • altered stool passage (straining, urgency, incomplete defecation);
  • abdominal bloating (although not persistent distension - a symptom of ovarian cancer);
  • symptoms made worse by eating;
  • passage of mucus.

The presence of other symptoms, such as low back pain, fatigue and bladder symptoms, supports the diagnosis of IBS. Patients suspected of having IBS should have an FBC, ESR, CRP and tests for coeliac disease to exclude other diagnoses.

Sigmoidoscopy is not routinely required.

Patients with alarm symptoms such as rectal bleeding, anaemia and weight loss should be referred for specialist assessment (see box).

Patients aged over 60 years presenting for the first time and those with atypical symptoms also warrant hospital referral.

Similarly, patients who have been diagnosed in primary care with a functional GI disorder but whose symptoms have worsened should be considered for referral to exclude an alternative diagnosis.


Guide for suspected colorectal cancer

At all ages

  • Definite, palpable, right-sided, abdominal mass.
  • Definite, palpable, rectal (not pelvic) mass.
  • Rectal bleeding with change in bowel habit to more frequent defecation or looser stools (or both) persistent over six weeks.
  • Iron-deficiency anaemia (haemoglobin concentration < 11.0g/dl in men or <10.0 g/dl in postmenopausal women) without obvious cause.

Over 60 years

  • Rectal bleeding persistently without anal symptoms (soreness, discomfort, itching, lumps, prolapse, pain).
  • Change of bowel habit to more frequent defecation or looser stools (or both), without rectal bleeding, and persistent for six weeks.


Section 4 Management
Treatment includes a thorough explanation of IBS and its symptoms. Being positive about the diagnosis reassures the patient that their symptoms are explainable and potentially treatable.

Drug treatments
The evidence for efficacy of drug therapies for IBS is weak.

Although there is evidence of benefit with antispasmodic drugs for abdominal pain and global assessment of symptoms, it is unclear whether antispasmodic subgroups are individually effective.

There is some evidence of benefit with antidepressants or bulking agents.

Global assessment of symptoms is a construct containing various dimensions.

For each patient, these will have a different weighting and treatment should be aimed at the most debilitating symptom. Stool problems are by definition part of the IBS symptom complex.

Bulking agents may improve constipation and can be used empirically, but should be evaluated at an early stage for individual benefit.

Antispasmodics are often used to treat abdominal pain. These drugs relax smooth muscle but vary in their specificity.

Antidepressants modify gut motility, and alter visceral nerve responses. These responses are usually seen long before effects on mood are evident.

5HT-active drugs
Two newer classes of compound that have shown promise in the treatment of IBS act on 5HT receptors. Early reports indicate that 5HT4-agonists improve constipation while 5HT3-antagonists reduce symptoms of diarrhoea.

However, their precise role in the primary care management of patients has yet to be established.

Diarrhoea and constipation
For patients with symptoms of diarrhoea, loperamide is effective. It slows large and small intestinal transit, and reduces stool frequency and urgency. Loperamide can also be taken prophylactically to avoid embarrassing incidents during work or leisure pursuits.

For patients with constipation, increased intake of dietary fibre, including those derived from cereals, fruits and vegetables has been shown to increase stool weight and accelerate gut motility.

Other treatments
Hypnosis, biofeedback and psychotherapy all have evidence of benefit in referred patients. A recent trial of CBT demonstrated its effectiveness in a general practice population.7



1. Spiller R, Aziz Q, Creed F et al. Guidelines on the Irritable Bowel Syndrome: Mechanisms and Practical Management. Gut 2007; 56: 1,770-98.

2. Guidelines for the management of IBS in general practice. Primary Care Society for Gastroenterology.

3. Whitehead W E, Crowell M D, Robinson J C et al. Effects of stressful life events on bowel symptoms: subjects with irritable bowel syndrome compared with subjects without bowel dysfunction. Gut 1992; 33: 825-30.

4. Neal K R, Hebden J, Spiller R. Prevalence of gastrointestinal symptoms six months after bacterial gastroenteritis and risk factors for development of the irritable bowel syndrome: postal survey of patients. BMJ 1997; 314: 779-82.

5. Rodriguez L A, Ruigomez A. Increased risk of irritable bowel syndrome after bacterial gastroenteritis: cohort study. BMJ 1999; 318: 565-6.

6. National Institute for Health and Clinical Excellence. Irritable bowel syndrome in adults. Diagnosis and management of irritable bowel syndrome in primary care. London: NICE 2008.

7. Kennedy T, Jones R, Darnley S et al. Cognitive behaviour therapy in addition to antispasmodic treatment for irritable bowel syndrome in primary care: randomised controlled trial. BMJ 2005; 331: 435; doi:10.1136/bmj.38545.505764.06

Further reading

  • Quartero A O, Meineche-Schmidt V, Muris J, Rubin G, de Wit N. Bulking agents, antispasmodic and antidepressant medication for the treatment of irritable bowel syndrome. The Cochrane Database of Systematic Reviews 2005, Issue 2.
  • April is International IBS Awareness Month. For more information see
  • For an archive of all GP clinical reviews visit

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