Opioid Receptor Agonist (Peripheral — Antidiarrhoeal) Pregnancy: eMC §4.6: safety in human pregnancy has not been established, although animal studies give no indication of teratogenic or embryotoxic properties; it is not advisable to administer loperamide in pregnancy, especially in the first trimester. Breast-feeding: small amounts may appear in human breast milk — not recommended during breast-feeding; advise breast-feeding women to consult their doctor. Effect on human fertility has not been evaluated.

Loperamide

Brand names: Imodium, Arret

Loperamide is an antimotility agent for symptomatic relief of acute and chronic diarrhoea where slowing the bowel is appropriate.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Acute diarrhoea (adults and children over 12 years): 4 mg (two 2 mg capsules) initially, followed by 2 mg (one capsule) after each loose stool. Usual dose 6-8 mg a day.

Route: Oral (capsules taken with liquid)

Frequency: Initial dose then one 2 mg capsule after each loose stool

Max: 16 mg (8 capsules) in 24 hours

CHRONIC DIARRHOEA (adults): patients may need widely differing amounts — starting dose 4-8 mg per day (two to four capsules) in divided doses depending on severity, adjusted according to response up to a maximum of 16 mg (eight capsules) daily. Once the daily maintenance dose is established, loperamide may be given on a twice-daily regimen; tolerance has not been observed so subsequent dose adjustment should be unnecessary. In acute diarrhoea, consider further investigation of the cause if there is no improvement within two days, and discontinue if there is no clinical improvement within 48 hours — advise the patient to consult their doctor. Treatment is symptomatic only; the priority in acute diarrhoea is prevention or reversal of fluid and electrolyte depletion, particularly in young children and frail/elderly patients. Discontinue promptly if constipation, abdominal distension or ileus develops; stop at the earliest sign of abdominal distension in patients with AIDS. Cardiac events including QT interval and QRS prolongation and torsade de pointes have been reported with overdose (some fatal), and overdose can unmask existing Brugada syndrome — patients must not exceed the recommended dose or duration. Elderly: no dose adjustment required. Hepatic impairment: use with caution (reduced first-pass metabolism may result in relative overdose and CNS toxicity). Contains lactose. PAEDIATRIC: the SPC gives a separate fixed-dose regimen for children aged 9 to 12 years (not weight-based) with a maximum duration of 5 days, and loperamide is contraindicated in children under 9 years of age — verify against a children's formulary before prescribing to under-18s.

Dose adjustments

Renal

eMC §4.2: no dose adjustment is required for patients with renal impairment.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Directions • drink plenty of clear fluids to help prevent dehydration caused by diarrhea • find right dose on chart. If possible, use weight to dose; otherwise use age. • shake well before using • use only enclosed dosing cup specifically designed for use with this product. Do not use any other dosing device. • mL = milliliter adults and children 12 years and over 30 mL after the first loose stool; 15 mL after each subsequent loose stool; but no more than 60 mL in 24 hours children 9-11 years (60-95 lbs) 15 mL after the first loose stool; 7.5 mL after each subsequent loose stool; but no more than 45 mL in 24 hours children 6-8 years (48-59 lbs) 15 mL after the first loose stool; 7.5 mL …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-04-11. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Known hypersensitivity to loperamide hydrochloride or to any of the excipients
Children less than 9 years of age
Where inhibition of peristalsis is to be avoided because of the risk of ileus, megacolon or toxic megacolon — in particular when ileus, constipation or abdominal distension develop
Acute ulcerative colitis
Bacterial enterocolitis caused by invasive organisms including Salmonella, Shigella and Campylobacter
Pseudomembranous colitis associated with broad-spectrum antibiotic use
Should not be used alone in acute dysentery (blood in stools with elevated body temperature)

Side effects

Constipation (2.7%) — common
Flatulence (1.7%) — common
Headache (1.2%) — common
Nausea (1.1%) — common
Dizziness — common; somnolence, dry mouth, abdominal pain/discomfort, vomiting, rash — uncommon
Ileus (including paralytic ileus), megacolon and toxic megacolon, urinary retention, anaphylaxis, bullous eruptions including Stevens-Johnson syndrome and toxic epidermal necrolysis — rare/not known

Interactions

P-glycoprotein inhibitors — quinidine or ritonavir with loperamide 16 mg single dose produced a 2 to 3-fold increase in loperamide plasma levels; clinical relevance at recommended doses is unknown (eMC §4.5)
Itraconazole (CYP3A4 and P-glycoprotein inhibitor) — with loperamide 4 mg single dose produced a 3 to 4-fold increase in loperamide plasma levels (eMC §4.5)

Clinical monograph

How it works

It is an opioid-receptor agonist acting locally on gut smooth muscle to slow transit, with minimal central effect at recommended doses.

Prescribing in practice

Avoid in acute bloody or inflammatory diarrhoea, suspected Clostridioides difficile, and active inflammatory bowel disease flare (risk of toxic megacolon).
Very high doses (overdose/misuse) can cause serious cardiac arrhythmias (MHRA).
Treat dehydration and address the underlying cause.

Monitoring

Review the cause of diarrhoea and hydration; no routine monitoring.

Counselling the patient

Do not exceed the recommended dose.
Seek help for blood in the stool, fever, or severe abdominal pain.
Keep up fluids.

Evidence & guidelines

Standard symptomatic treatment for non-inflammatory diarrhoea, with an MHRA warning about cardiac effects in overdose.

Reference: MHRA Drug Safety Update 2017 (loperamide cardiac events); NICE CG61 (IBS); NICE CKS Diarrhoea; SPC Imodium; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways