Irritable bowel syndrome

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.

References

1.Indian Society of Gastroenterology — Irritable Bowel Syndrome Practice Guidelines (2023); ACG Clinical Guideline: Management of Irritable Bowel Syndrome (2021) (2023)
2.ACG Clinical Guideline: Management of Irritable Bowel Syndrome. American Journal of Gastroenterology (2021)