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Health condition · Clinically reviewed

Chronic diarrhoea, the causes, the tests and the treatments that actually help.

Loose stool for more than four weeks deserves a proper look - not another course of loperamide. A structured work-up usually finds the reason.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against BSG, NICE and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK gastroenterology practice including SeHCAT, faecal calprotectin and bile acid diarrhoea care.

Key facts

Chronic diarrhoea at a glance.

The essentials, in plain English - what it is, the main categories, and how UK gastroenterologists work it up today.

  • What it is

    Loose or watery stool more than three times a day for over four weeks - often with increased urgency, volume or nocturnal disturbance.

  • Broad categories

    Functional (IBS-D), inflammatory (IBD, microscopic colitis), malabsorption (coeliac, bile acid, pancreatic), infective, endocrine, medication-related and neoplastic.

  • Types by mechanism

    Watery (secretory or osmotic), inflammatory (blood and mucus) and fatty (steatorrhoea) - each points at a different set of causes.

  • First-line tests

    Bloods (FBC, ferritin, coeliac serology, TSH), stool culture, faecal calprotectin and faecal elastase - simple, quick, high yield.

  • Gold-standard test

    Colonoscopy with random biopsies for red flags or suspected microscopic colitis - see our colonoscopy guide.

  • Bile acid diarrhoea

    Under-recognised - up to a third of people labelled IBS-D actually have BAM. SeHCAT is the definitive UK test.

Why this guide matters

A cause, not just a label.

Chronic diarrhoea is common, and often mislabelled as IBS. Getting to the right diagnosis changes the treatment - and the outcome.

  • Categories drive the plan

    Functional, inflammatory, malabsorptive, infective, endocrine, medication-related and neoplastic - each has its own set of tests and treatments.

  • Red flags cannot be ignored

    Blood, nocturnal symptoms, weight loss and anaemia are 2-week-wait indications - they change the pace and depth of the work-up.

  • Missed diagnoses are common

    Bile acid diarrhoea, microscopic colitis and coeliac disease are frequently overlooked and are all very treatable.

How the diagnosis is made

From first symptoms to a clear diagnosis.

The steps a UK GP or gastroenterologist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    Focused history

    Timing, nocturnal episodes, blood, weight loss, medications, travel, diet and prior surgery - the story usually narrows the differential fast.

  2. 02

    Assessing

    Examination and PR

    Weight, hydration, abdominal exam and a digital rectal examination to check for masses, blood or overflow.

  3. 03

    Assessing

    Stool studies

    Microscopy, culture, C. difficile toxin, faecal calprotectin (IBD screen), faecal elastase (pancreatic exocrine) and FIT.

  4. 04

    Confirming

    Bloods

    FBC, ferritin, CRP, U&Es, LFTs, TSH, coeliac serology, immunoglobulins and HIV where appropriate.

  5. 05

    Confirming

    Colonoscopy with biopsies

    Gold standard for red flags and suspected microscopic colitis - random biopsies of macroscopically normal mucosa are essential.

  6. 06

    Specialist

    Targeted specialist tests

    SeHCAT for bile acid diarrhoea, breath tests for SIBO, upper GI endoscopy with duodenal biopsy, and hormone panels for suspected NETs.

  7. 07

    Specialist

    Small bowel imaging

    MRI enterography or capsule endoscopy for suspected small bowel disease when standard tests are unrevealing.

Typical timeline: first visit to a working diagnosis in weeks, not months.

Symptoms

What chronic diarrhoea actually looks like.

The pattern of stool, timing, urgency and associated features often tell you which of the ten categories you are dealing with.

  • Watery stool

    Frequent loose or liquid stool - the most common presentation and can be secretory or osmotic in origin.

  • Urgency and incontinence

    Sudden, hard-to-defer urges - a major quality-of-life burden and worth flagging early to your clinician.

  • Blood or mucus

    Points strongly at inflammatory disease - IBD, colitis or, in older patients, colorectal cancer until proven otherwise.

  • Steatorrhoea

    Pale, oily, floating stool that is hard to flush - suggests fat malabsorption from pancreatic or small bowel disease.

  • Nocturnal diarrhoea

    Waking at night to open the bowels is not a functional feature - it points at organic disease and warrants investigation.

  • Weight loss and fatigue

    Unintended weight loss with chronic diarrhoea needs prompt work-up for malabsorption, inflammation or malignancy.

  • Bloating and cramping

    Common in IBS-D, SIBO, coeliac disease and lactose intolerance - the pattern and triggers help sort them out.

  • Red flag - blood, nocturnal or weight loss

    Rectal bleeding, waking at night, anaemia, weight loss, family history of bowel cancer or a palpable mass - urgent referral.

Treatment

How chronic diarrhoea is treated in the UK.

Cause-specific therapy first, then symptomatic control, dietary work and, where needed, advanced options like FMT or octreotide.

  • Treat the specific cause

    Coeliac needs a strict gluten-free diet, IBD needs 5-ASA, steroids, immunomodulators or biologics, BAM needs bile acid sequestrants - the diagnosis drives the plan.

  • Loperamide

    First-line symptom control - safe, effective and can be titrated to stool form. Not for suspected inflammatory or infective diarrhoea with fever.

  • Bile acid sequestrants

    Colestyramine, colesevelam or colestipol for bile acid diarrhoea - often transformative when the diagnosis is right.

  • Rifaximin

    A non-absorbed antibiotic used for SIBO and for diarrhoea-predominant IBS with bloating.

  • Budesonide

    The mainstay of microscopic colitis care - a targeted steroid with limited systemic effect, usually alongside stopping the offending drug.

  • Pancreatic enzyme replacement

    Creon (pancreatin) with meals for exocrine pancreatic insufficiency - a PPI is often added to protect the enzymes.

  • Dietary work with a dietitian

    Low-FODMAP, lactose-free or specific elimination diets - much more effective when structured with a specialist rather than tried alone.

  • Advanced options

    Octreotide for carcinoid or refractory secretory diarrhoea, sacral nerve stimulation for faecal incontinence, and FMT for recurrent C. difficile.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or gastroenterologist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • British Society of Gastroenterology (BSG). Guidelines on the investigation of chronic diarrhoea.

  • NICE. Irritable bowel syndrome in adults (CG61) and quality standards.

  • NICE. Suspected cancer: recognition and referral (NG12) - lower GI 2WW criteria.

  • BSG. Guidelines for the investigation and management of bile acid diarrhoea and microscopic colitis.

Red flags

When chronic diarrhoea needs urgent attention.

Most chronic diarrhoea is managed in primary care with specialist input as needed. These features change the pace - and often the diagnosis.

  • Rectal bleeding

    Any visible blood with chronic diarrhoea needs prompt colonoscopy - do not assume haemorrhoids.

  • Nocturnal diarrhoea

    Waking at night to open the bowels is an organic red flag - functional bowel disease rarely does this.

  • Unintentional weight loss

    Weight loss alongside chronic diarrhoea points at malabsorption, inflammation or cancer and needs urgent work-up.

  • Iron-deficiency anaemia

    A low ferritin with diarrhoea in an adult warrants both upper and lower GI investigation.

  • Family history of bowel cancer

    A first-degree relative with colorectal cancer lowers the threshold for referral and colonoscopy.

  • Palpable abdominal or rectal mass

    Any palpable mass is a 2-week-wait indication under NG12 - refer immediately.

  • Recent travel or antibiotics

    Think parasitic infection after travel and C. difficile after recent antibiotic exposure.

  • Immunosuppression

    HIV, chemotherapy or checkpoint inhibitors change both the differential and the urgency - low threshold for specialist review.

  • Fever, dehydration or severe pain

    Systemic upset with chronic diarrhoea needs same-day assessment - especially in the frail or elderly.

Living with it

A treatable condition, with a clear pathway.

Four things that make the biggest difference day to day - a symptom diary, structured dietary work, deliberate rehydration and not accepting a stale diagnosis.

A quiet reminder

A precise diagnosis unlocks a precise treatment.

Blanket labels rarely help. Small, targeted changes - based on the right diagnosis - almost always do.

  1. 01 Diary

    Keep a food and symptom diary

    Two weeks of honest notes will often show the pattern - a diary is one of the highest-yield things you can do.

  2. 02 Diet

    Work with a dietitian, not alone

    Low-FODMAP and elimination diets are powerful but should be structured and time-limited - a dietitian keeps them safe.

  3. 03 Hydration

    Rehydrate deliberately

    Oral rehydration solutions beat plain water when losses are large - and are especially important in older adults.

  4. 04 Escalate

    Do not accept "just IBS"

    If red flags appear, or the diagnosis has not been revisited in years, ask for a fresh look - BAM, microscopic colitis and coeliac are often missed.

Frequently asked

Everything we get asked about chronic diarrhoea.

Quick answers on causes, tests, red flags and treatments.

  • What counts as chronic diarrhoea?

    Loose or watery stool more than three times a day for more than four weeks. Increased frequency, urgency, nocturnal disturbance and weight loss are all significant features that push the work-up along.

  • Is it always IBS?

    No. IBS-D is common but so are bile acid diarrhoea, microscopic colitis, coeliac disease, SIBO and inflammatory bowel disease. A proper work-up matters because these need very different treatments.

  • What tests will I need?

    Usually bloods (including coeliac serology, TSH and ferritin), stool tests (culture, C. difficile, calprotectin and elastase), and often a colonoscopy with biopsies. SeHCAT, breath tests and small bowel imaging are added when the picture points there.

  • When should I worry about cancer?

    Rectal bleeding, weight loss, anaemia, a palpable mass, a strong family history or a change in bowel habit in someone over 60 all lower the threshold. These meet the 2-week-wait referral criteria under NG12.

  • What is bile acid diarrhoea?

    A common but under-recognised cause where excess bile acids reach the colon and drive watery diarrhoea - often after gallbladder removal or terminal ileal disease. SeHCAT confirms it and bile acid sequestrants treat it well.

  • Can medications cause it?

    Yes - metformin, PPIs, SSRIs, magnesium supplements, colchicine, laxatives, some antibiotics and checkpoint immunotherapies are common culprits. A careful medication review is part of every work-up.

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