Red Flags
- Onset of bowel symptoms after age 50; weight loss; nocturnal symptoms; rectal bleeding; iron-deficiency anaemia — colonoscopy and structural workup before labelling IBS[1]
- Family history of colorectal cancer, IBD, or coeliac disease — lower threshold for colonoscopy and serology[1]
- Persistent diarrhoea with raised CRP, faecal calprotectin >50 µg/g, or hypoalbuminaemia — exclude IBD before treating as IBS-D[2]
- Severe abdominal pain with fever, vomiting, or peritonism — emergency surgical evaluation; not IBS[1]
First-line treatment
Interventions
- Patient education and reassurance[2]Explain IBS as a brain-gut disorder with real symptoms and no structural pathology; positive diagnosis improves outcomes more than extensive investigation
- Low FODMAP diet (4–6 week trial, then reintroduction)[2]Dietitian-led; significant symptom improvement in 50–70% of IBS; reintroduce systematically to identify trigger groups (fructans, lactose, polyols, GOS, fructose); avoid long-term restrictive diet
- Soluble fibre (psyllium/ispaghula)[2]First-line in IBS-C and mixed IBS; 10–20 g/day in divided doses with adequate water; insoluble fibre (bran) often worsens bloating and pain
- Gut-directed psychotherapy[2]Cognitive behavioural therapy or gut-directed hypnotherapy for refractory or psychologically distressed IBS; effect size comparable to pharmacotherapy
First-line drug therapy
| Drug | Class | Adult | Paediatric | Notes |
|---|---|---|---|---|
| Hyoscine butylbromide or dicyclomine[1] | Antispasmodic (anticholinergic) | Hyoscine 10–20 mg PO TDS PRN; dicyclomine 10–20 mg PO TDS PRN | — | Symptomatic relief of cramping abdominal pain; dry mouth, blurred vision, urinary retention; avoid in glaucoma and BPH |
| Peppermint oil (enteric-coated)[2] | Smooth muscle relaxant | 180–225 mg PO TDS before meals | — | Effective for IBS pain and bloating; may worsen reflux; use enteric-coated to avoid heartburn |
| Loperamide (IBS-D)[2] | Peripheral µ-opioid agonist | 2 mg PO PRN before known triggers; max 16 mg/day | — | First-line for diarrhoea symptom control in IBS-D; does not address pain — combine with antispasmodic if needed |
| Rifaximin (IBS-D without constipation)[2] | Non-absorbable rifamycin antibiotic | 550 mg PO TDS × 14 days; may repeat once if relapse within 18 weeks | — | Modest benefit in non-constipation IBS; reserved for refractory cases due to cost |
| Polyethylene glycol (IBS-C)[2] | Osmotic laxative | 17 g PO daily, titrate | — | First-line for constipation symptoms; improves stool frequency more than abdominal pain |
| Linaclotide (IBS-C)[2] | Guanylate cyclase-C agonist | 290 µg PO once daily 30 min before breakfast | — | Refractory IBS-C; diarrhoea is dose-limiting; superior to PEG for global IBS-C symptoms including pain |
| Low-dose tricyclic antidepressant (amitriptyline)[2] | Tricyclic antidepressant (neuromodulator) | 10–25 mg PO at night; titrate to 50 mg as tolerated | — | IBS-D with refractory pain; constipating side effect helpful in IBS-D, problematic in IBS-C; ATLANTIS trial confirmed benefit |
Hyoscine butylbromide or dicyclomine[1]
Antispasmodic (anticholinergic)
- Adult
- Hyoscine 10–20 mg PO TDS PRN; dicyclomine 10–20 mg PO TDS PRN
- Paediatric
- —
Symptomatic relief of cramping abdominal pain; dry mouth, blurred vision, urinary retention; avoid in glaucoma and BPH
Peppermint oil (enteric-coated)[2]
Smooth muscle relaxant
- Adult
- 180–225 mg PO TDS before meals
- Paediatric
- —
Effective for IBS pain and bloating; may worsen reflux; use enteric-coated to avoid heartburn
Loperamide (IBS-D)[2]
Peripheral µ-opioid agonist
- Adult
- 2 mg PO PRN before known triggers; max 16 mg/day
- Paediatric
- —
First-line for diarrhoea symptom control in IBS-D; does not address pain — combine with antispasmodic if needed
Rifaximin (IBS-D without constipation)[2]
Non-absorbable rifamycin antibiotic
- Adult
- 550 mg PO TDS × 14 days; may repeat once if relapse within 18 weeks
- Paediatric
- —
Modest benefit in non-constipation IBS; reserved for refractory cases due to cost
Polyethylene glycol (IBS-C)[2]
Osmotic laxative
- Adult
- 17 g PO daily, titrate
- Paediatric
- —
First-line for constipation symptoms; improves stool frequency more than abdominal pain
Linaclotide (IBS-C)[2]
Guanylate cyclase-C agonist
- Adult
- 290 µg PO once daily 30 min before breakfast
- Paediatric
- —
Refractory IBS-C; diarrhoea is dose-limiting; superior to PEG for global IBS-C symptoms including pain
Low-dose tricyclic antidepressant (amitriptyline)[2]
Tricyclic antidepressant (neuromodulator)
- Adult
- 10–25 mg PO at night; titrate to 50 mg as tolerated
- Paediatric
- —
IBS-D with refractory pain; constipating side effect helpful in IBS-D, problematic in IBS-C; ATLANTIS trial confirmed benefit
Safety-net
- Return for review if you develop bleeding from the back passage, significant unintended weight loss, fever, or symptoms that wake you from sleep — these are not IBS features[1]
- Low-FODMAP diet should not be lifelong — reintroduce trigger groups systematically with a dietitian after 4–6 weeks to avoid nutritional deficiency and gut dysbiosis[2]
- Stress, sleep loss, and gastrointestinal infection are common IBS triggers — tracking flares with a symptom diary helps identify modifiable factors[2]
Referral criteria
- Any alarm feature (bleeding, weight loss, anaemia, age ≥50 with new symptoms, nocturnal symptoms)Gastroenterology with colonoscopy[1]
- Refractory IBS despite first-line lifestyle, fibre, antispasmodics, and subtype-specific therapy at 8–12 weeksGastroenterology and consider gut-directed psychotherapy referral[2]
- Suspected coeliac disease or IBD on initial workup (positive serology, raised calprotectin, anaemia)Gastroenterology with biopsy and endoscopy[2]
- Significant psychological distress, depression, or somatisation interfering with managementMental health and gut-directed psychotherapy[2]
Clinical summary
Diagnosis by Rome IV criteria with limited investigation in young patients without alarm features; subtype-directed management of IBS-D, IBS-C, IBS-M.