Skip to textbook content
Doctor’s PassportTextbook
TopicsAll topics

Loading topic navigation…

Textbook navigation
TopicsAll topics

Loading topic navigation…
Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Irritable bowel syndrome

Gastroenterology and hepatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
!
Escalate

IBS does not cause shock, peritonism, sepsis, obstruction, major rectal bleeding or profound dehydration. A patient with those findings needs acute assessment for another diagnosis. New iron-deficiency anaemia, an abdominal or rectal mass, persistent unexplained weight loss or a qualifying change in bowel habit should enter the current NICE suspected-cancer pathway rather than being absorbed into an old IBS label.

Synopsis

Make a confident positive diagnosis of irritable bowel syndrome after proportionate exclusion of important disease, then deliver phenotype-led dietary, pharmacological and behavioural care with explicit safety-netting.

  • IBS is a disorder of gut-brain interaction characterised by recurrent abdominal pain linked to defaecation or altered stool frequency or form, not a diagnosis defined by bloating alone.
  • Classify the current pattern as constipation-predominant, diarrhoea-predominant, mixed or unclassified because treatment follows the dominant stool problem and can change over time.
  • Make a positive diagnosis when the symptom pattern, examination and limited tests fit; repeated normal scans and colonoscopies can reinforce uncertainty rather than improve care.
  • Check full blood count, inflammatory markers and coeliac serology in a typical presentation, adding faecal calprotectin or cancer-pathway testing only when age and features justify them.
  • General measures include regular meals, hydration, physical activity and soluble rather than insoluble fibre; bran frequently worsens bloating and pain.
  • A low-FODMAP or other exclusion diet should be structured by a clinician with dietary expertise and followed by reintroduction, not continued as an unsupervised ever-shrinking food list.
  • Use antispasmodics for pain, loperamide for diarrhoea and suitable laxatives for constipation, titrating towards a soft formed stool rather than complete symptom abolition.
  • Low-dose tricyclic treatment acts as a gut-brain neuromodulator in persistent pain; explain the rationale so the patient does not hear that symptoms are imagined.

Key red flags

Inflammatory mimic

Blood mixed with stool, night-time diarrhoea, fever, raised inflammatory markers, perianal disease or progressive weight loss is discordant and requires assessment for IBD, infection or microscopic colitis.

Cancer warning pattern

A palpable mass, iron-deficiency anaemia, rectal bleeding or an age- and symptom-qualified bowel change must be assessed using current NG12 and FIT pathways rather than explained by longstanding IBS.

Investigation priorities

01
Full blood count and inflammatory markersFirst step

Look for anaemia and objective inflammation that would make uncomplicated IBS less likely.

Management branches

Positive diagnosisConfirm pattern and exclude proportionately

Recurrent abdominal pain and altered bowel habit suggest a disorder of gut-brain interaction.

  1. Map pain to defaecation and stool change, record Bristol form and duration, examine the abdomen and rectum when clinically indicated, and ask about warning features.
  2. Request full blood count, inflammatory markers and coeliac serology, adding calprotectin, infection testing, FIT or endoscopy only for a defined indication.
  3. Name the current IBS subtype, explain gut-brain mechanisms in neutral language and acknowledge that a positive diagnosis does not mean symptoms are psychological invention.
  4. Agree one functional goal, one treatment target and explicit triggers for reassessment, documenting why further investigation is or is not needed.
First-line careTreat the dominant phenotype

Typical IBS is established without a current red flag or untreated organic mimic.

  1. Begin regular meals, adequate fluid, graded physical activity and a review of caffeine, alcohol, fizzy drinks, sorbitol and fibre, avoiding a universal restrictive checklist.
  2. For constipation favour soluble fibre and an appropriate laxative; for diarrhoea consider

Key medicines

LoperamideUse the current formulary starting regimen for IBS-D and let the patient titrate cautiously towards Bristol type 4 rather than a fixed maximal schedule.Avoid during acute bloody diarrhoea, fever, suspected ileus or severe inflammatory colitis. Excess dosing can cause constipation and serious cardiac toxicity; review continued need and response.
Soluble fibre or laxativeIntroduce ispaghula or another suitable constipation treatment gradually with fluid, then adjust to a soft formed stool using the local formulary sequence.Escalation may increase gas or pain; avoid bulk agents in suspected obstruction. NICE discourages lactulose in IBS because it can worsen bloating, and persistent outlet symptoms need pelvic-floor assessment.
Open full textbook →Answer 2 questions
Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE CG61 irritable bowel syndromePositive diagnosis, core investigations, diet, medicines, psychological therapy and follow-up.
  • BSG irritable bowel syndrome guidelineContemporary disorder-of-gut-brain-interaction framework and secondary-care management.
  • NICE faecal calprotectin guidanceAppropriate use of calprotectin to distinguish inflammatory from non-inflammatory bowel disease.
  • NICE coeliac disease guidelineWho to test and how to perform serology while gluten is being consumed.
  • NICE NG12 suspected colorectal cancerCurrent referral and FIT pathways for warning features that should not be labelled IBS.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
loperamide
; for episodic pain consider an antispasmodic and titrate by response.
  • Use a symptom and food record for a limited period, altering one intervention at a time so benefit and harm can be attributed.
  • Review after an agreed interval for stool form, pain, urgency, sleep, participation and adverse effects, then stop ineffective measures rather than accumulating treatments.