guidelines

irritable bowel syndrome (ibs) in adults

nice-based ibs diagnosis (positive criteria), minimal tests to exclude red flags, stepwise diet/lifestyle strategy, and symptom-targeted pharmacology including low-dose tca guidance.

last reviewed: 2026-02-13
based on: NICE CG61 (published 23 Feb 2008; last updated 04 Apr 2017; surveillance decision Apr 2025)
reviewer: Dr Kola Tytler MBBS CertHE MBA MRCGP
view official NICE source

Diagnosis: make it positive, not a diagnosis of exclusion

NICE-style IBS diagnosis: abdominal pain/discomfort with altered bowel habit, often associated with bloating, and symptom pattern that fits IBS (rather than red-flag disease). Use clinical judgement and a focused baseline screen.

Red flags for urgent work-up / referral: unintentional weight loss, rectal bleeding, anaemia, abdominal/rectal mass, nocturnal symptoms, family history of colorectal cancer/IBD, persistent fever, or new change in bowel habit in older patients.

Minimum tests (typical NICE approach)

  • Full blood count.
  • Inflammatory marker (CRP) and/or ESR.
  • Coeliac serology.
  • Consider faecal calprotectin in suspected IBD pathways (local protocol).

Do not over-investigate low-risk classic IBS; use red flags and risk to drive escalation.

Management: diet, lifestyle, then symptom targeting

  • Diet first: regular meals; limit caffeine/alcohol; adjust fibre (often reduce insoluble fibre; consider soluble fibre e.g. ispaghula); consider a structured low FODMAP trial with dietetic support.
  • Pain/bloating: antispasmodics (e.g. hyoscine butylbromide, mebeverine) as needed.
  • Constipation: consider osmotic laxatives; avoid lactulose if it worsens bloating; titrate to response.
  • Diarrhoea: loperamide titrated to stool pattern; consider bile acid malabsorption if refractory (specialist pathways).

Low-dose antidepressants for IBS pain (NICE CG61)

Tricyclics (TCA): consider low-dose TCAs for abdominal pain/discomfort, starting with amitriptyline 5–10 mg once nightly and increasing slowly, if needed, up to 30 mg once nightly. Review response at 4 weeks, then 6–12 monthly.

If TCA not suitable/effective: consider SSRIs (specialist/shared-care context), particularly where mood symptoms co-exist.

Frequently asked questions

Do I need colonoscopy for all IBS?
No. Use red flags and age/risk factors to decide. Classic IBS in a low-risk patient usually needs only a focused baseline screen (FBC, CRP/ESR, coeliac serology) plus safety-netting.
How do I explain low-dose amitriptyline to patients?
Frame it as “neuromodulation” for gut–brain pain pathways at much lower doses than for depression. Start low (5–10 mg at night), titrate slowly, and warn about dry mouth/sedation.
When should I re-check and step up?
If symptoms persist despite diet and symptom-targeted medications, consider dietitian-led low FODMAP, psychological therapies, and specialist review where red flags, refractory symptoms, or diagnostic uncertainty exist.

Transparency

This page is an educational, clinician-written summary of publicly available NICE guidance intended for trained healthcare professionals. It uses original wording (not copied text) and should be used alongside the full NICE source, local pathways, and clinical judgement. Doses provided are for general reference; always check the BNF/SPC.