Irritable Bowel Syndrome
Summary
Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterised by recurrent abdominal pain associated with defecation or change in bowel habit, in the absence of organic disease. Diagnosis is clinical using Rome IV criteria. IBS is classified as IBS-C (constipation-predominant), IBS-D (diarrhoea-predominant), IBS-M (mixed), or IBS-U (unsubtyped). Investigations are limited in typical presentations but should exclude coeliac disease. Treatment is symptom-directed: dietary modification (low FODMAP), antispasmodics, laxatives or antidiarrhoeals, and neuromodulators. Psychological therapies (CBT, gut-directed hypnotherapy) are effective.
Key Facts
- Definition: Functional disorder with abdominal pain + altered bowel habit (Rome IV)
- Prevalence: 10-15% of adults; most common GI diagnosis in primary care
- Demographics: F:M 2:1; peak 20-40 years
- Subtypes: IBS-C, IBS-D, IBS-M, IBS-U
- Gold Standard Investigation: Clinical diagnosis (Rome IV); exclude coeliac
- First-line Treatment: Dietary advice (low FODMAP), symptom-directed therapy
- Prognosis: Chronic, relapsing-remitting; does not progress to organic disease
Clinical Pearls
Rome IV Pearl: Abdominal pain at least 1 day/week for 3 months, associated with 2+ of: related to defecation, change in stool frequency, change in stool form.
Coeliac Pearl: NICE recommends testing for coeliac disease in all patients meeting IBS criteria (serological testing).
FODMAP Pearl: Low FODMAP diet is effective in 50-80% of IBS patients. Dietitian-led implementation improves success.
Red Flag Pearl: IBS is a diagnosis of exclusion in older patients. Any red flag mandates investigation.
Psychological Pearl: Gut-brain axis is central. CBT and hypnotherapy have good evidence in IBS.
Why This Matters Clinically
IBS is extremely common and significantly impacts quality of life. Recognising when to investigate vs when to confidently diagnose clinically, and providing effective symptom management, improves outcomes.
Prevalence
- 10-15% of adults
- Most common GI condition in primary care
- Only 30% seek medical attention
Demographics
- Female predominance 2:1
- Peak age 20-40 years
- Less common in elderly (consider alternative diagnoses)
Risk Factors
| Factor | Association |
|---|---|
| Female sex | 2x risk |
| Age less than 50 | More common |
| Prior GI infection (post-infectious IBS) | 10% after gastroenteritis |
| Psychological factors | Anxiety, depression, stress |
| Adverse childhood events | Increased risk |
Mechanism Overview
Multifactorial:
-
Visceral Hypersensitivity
- Increased perception of normal bowel activity
- Lowered pain thresholds
-
Altered Gut Motility
- Dysmotility patterns
- Contributes to constipation or diarrhoea
-
Gut-Brain Axis Dysfunction
- Bidirectional communication between gut and CNS
- Central sensitisation
- Explains stress-symptom relationship
-
Altered Gut Microbiome
- Dysbiosis in some patients
- Post-infectious IBS supports microbiome role
-
Low-Grade Inflammation
- Increased mast cells in mucosa
- Especially post-infectious
-
Dietary Factors
- FODMAPs fermented by gut bacteria
- Gas production, osmotic effects
Subtypes
| Subtype | Stool Pattern |
|---|---|
| IBS-C | Bristol 1-2 (hard) predominant |
| IBS-D | Bristol 6-7 (loose) predominant |
| IBS-M | Both hard and loose |
| IBS-U | Neither pattern predominant |
Rome IV Diagnostic Criteria
Recurrent abdominal pain, on average, at least 1 day/week in last 3 months, associated with 2 or more of:
Criteria fulfilled for last 3 months with symptom onset at least 6 months prior.
Symptoms
| Symptom | Character |
|---|---|
| Abdominal pain | Crampy, lower abdomen, relieved by defecation |
| Bloating | Very common, worse by evening |
| Altered bowel habit | Constipation, diarrhoea, or alternating |
| Mucus in stool | Common |
| Urgency | Especially IBS-D |
| Incomplete evacuation | Common |
Red Flags (Must Exclude Organic Disease)
[!CAUTION]
- Age greater than 50 with new symptoms
- Unintentional weight loss
- Rectal bleeding
- Family history colorectal cancer or IBD
- Anaemia
- Nocturnal symptoms waking patient
- Progressive symptoms
- Rectal/abdominal mass
Usually Normal
- No specific abnormality in IBS
- Abdominal examination typically unremarkable
- Mild tenderness lower abdomen may be present
Essential Checks
- Weight (exclude weight loss)
- Abdominal examination (masses)
- Rectal examination if red flags
Investigations in Typical IBS
| Test | Purpose |
|---|---|
| FBC | Exclude anaemia |
| CRP/ESR | Exclude inflammation (suggests IBD) |
| Coeliac serology (IgA-TTG + total IgA) | Exclude coeliac disease |
NICE: In typical IBS without red flags, these tests are usually sufficient.
If Red Flags or Atypical
- Colonoscopy (if age greater than 50, family history, bleeding)
- Faecal calprotectin (to exclude IBD)
- Stool microscopy and culture (if diarrhoea-predominant)
- TFTs
- Consider hydrogen breath test (SIBO, lactose intolerance)
What NOT to Do
- Excessive investigation in typical IBS causes anxiety and may reinforce illness behaviour
Management Algorithm
IBS DIAGNOSIS (ROME IV, RED FLAGS EXCLUDED)
↓
┌──────────────────────────────────────────────────────────────┐
│ GENERAL APPROACH │
│ - Reassure: IBS is real but not dangerous │
│ - Explain gut-brain connection │
│ - Dietary and lifestyle advice │
│ - Treat dominant symptom │
└──────────────────────────────────────────────────────────────┘
↓
┌──────────────────────────────────────────────────────────────┐
│ DIETARY │
│ - Regular meals, adequate fluids │
│ - Limit caffeine, alcohol, fizzy drinks │
│ - Low FODMAP diet (dietitian-guided, 4-8 weeks trial) │
│ - Fibre: soluble (ispaghula) if constipation; limit │
│ insoluble (bran) if bloating │
└──────────────────────────────────────────────────────────────┘
↓
┌──────────────────────────────────────────────────────────────┐
│ SYMPTOM-DIRECTED PHARMACOTHERAPY │
├──────────────────────────────────────────────────────────────┤
│ PAIN/BLOATING: │
│ - Antispasmodics: hyoscine, mebeverine, peppermint oil │
│ │
│ IBS-C: │
│ - Osmotic laxatives (macrogol) │
│ - Linaclotide (if laxatives fail) │
│ │
│ IBS-D: │
│ - Loperamide (as needed, not prophylactically) │
│ - Bile acid sequestrant if BAM suspected │
│ │
│ NEUROMODULATORS (if first-line fails): │
│ - Low-dose TCA (amitriptyline 10-30mg nocte) particularly │
│ for pain-predominant IBS │
│ - SSRI if anxiety/depression comorbid │
└──────────────────────────────────────────────────────────────┘
↓
┌──────────────────────────────────────────────────────────────┐
│ PSYCHOLOGICAL THERAPIES │
│ - CBT (good evidence, especially if psychological distress) │
│ - Gut-directed hypnotherapy (strong evidence) │
│ - Mindfulness-based therapy │
└──────────────────────────────────────────────────────────────┘
Pharmacotherapy
| Symptom | Drug | Notes |
|---|---|---|
| Pain/bloating | Mebeverine 135mg TDS | Antispasmodic |
| Pain/bloating | Peppermint oil capsules | Evidence-based |
| Constipation | Macrogol (Movicol) | Osmotic laxative |
| Constipation (refractory) | Linaclotide 290mcg OD | Secretagogue; take 30 min before meal |
| Diarrhoea | Loperamide 2-4mg PRN | Avoid regular use |
| Pain + diarrhoea | Amitriptyline 10-30mg nocte | TCA; start low |
| Pain + anxiety | SSRI (sertraline, citalopram) | If depression/anxiety comorbid |
Low FODMAP Diet
FODMAP: Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols
- High FODMAP foods: onion, garlic, wheat, lactose, apples, pears, legumes
- Elimination phase (4-8 weeks), then structured reintroduction
- Dietitian-supervised for best outcomes
- 50-80% response rate
- IBS does NOT progress to IBD or cancer
- Main complications are quality of life impairment
- Impact on work, social function
- Psychological comorbidity common
Natural History
- Chronic, relapsing-remitting
- Symptoms often persist for years but may wax and wane
- 30-50% improve over time
Treatment Outcomes
- Many respond to dietary modification
- Neuromodulators effective in 30-40%
- Psychological therapies: 50-60% response
Key Guidelines
-
NICE Guideline CG61. Irritable bowel syndrome in adults — 2008 (updated 2017)
-
BSG Guidelines on IBS — Vasant DH et al. Gut. 2021
-
ACG Clinical Guideline: IBS — Lacy BE et al. Am J Gastroenterol. 2021
-
Rome IV Criteria — Drossman DA. Gastroenterology. 2016
Key Evidence
Low FODMAP diet:
- RCTs demonstrate significant symptom improvement
- PMID: 27569451
TCAs:
- Meta-analysis shows efficacy for IBS symptoms
- PMID: 26416187
Gut-directed hypnotherapy:
- Long-term efficacy demonstrated
- PMID: 12496174
What is IBS?
IBS is a common condition affecting how your gut works. It causes pain, bloating, and changes in your bowel habit (diarrhoea, constipation, or both). The gut is sensitive and reacts more to normal stimuli.
Is it serious?
No - IBS is uncomfortable but not dangerous. It does not lead to cancer or other serious conditions.
What causes it?
The exact cause isn't known, but stress, diet, and gut sensitivity all play a role. There's a strong connection between your brain and gut.
Treatment
- Dietary changes (especially low FODMAP - your GP or dietitian can guide you)
- Medications for specific symptoms (antispasmodics, laxatives, antidiarrhoeals)
- Stress management and psychological support if needed
What can I do?
- Regular meals, good hydration
- Identify and avoid trigger foods
- Regular exercise helps gut motility and stress
- Don't suffer in silence - effective treatments exist
-
NICE Guideline CG61. Irritable bowel syndrome in adults. 2008.
-
Vasant DH et al. British Society of Gastroenterology guidelines on the management of IBS. Gut. 2021;70(7):1214-1240. PMID: 33903147
-
Lacy BE et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116(1):17-44. PMID: 33315591
-
Halmos EP et al. A diet low in FODMAPs reduces symptoms of IBS. Gastroenterology. 2014;146(1):67-75. PMID: 24076059
-
Ford AC et al. Efficacy of antidepressants and psychological therapies in IBS: systematic review and meta-analysis. Gut. 2014;63(5):753-760. PMID: 23911555
-
Drossman DA. Rome IV Functional Gastrointestinal Disorders. Gastroenterology. 2016;150(6):1262-1279.
Viva Points
"IBS is a functional GI disorder diagnosed clinically with Rome IV criteria: recurrent abdominal pain 1+ day/week for 3 months, associated with defecation or stool changes. Exclude red flags and coeliac disease. Treat with dietary modification (low FODMAP), antispasmodics. TCAs for pain. Psychological therapies (CBT, hypnotherapy) are effective. IBS doesn't progress to organic disease."
Common Mistakes
- ❌ Over-investigating typical IBS
- ❌ Forgetting to test for coeliac disease
- ❌ Missing red flags requiring further investigation
- ❌ Not considering psychological therapies
- ❌ Diagnosing IBS in elderly without investigation
Last Reviewed: 2026-01-01 | MedVellum Editorial Team