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Opioid Receptor Agonist (Peripheral — Antidiarrhoeal)

Loperamide

Brand names: Imodium, Arret

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

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses 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.

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. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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