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Antidiarrhoeal (Opioid Receptor Agonist — Peripheral)

Loperamide Hydrochloride

Brand names: Imodium, Arret

Loperamide is an antimotility agent used for the symptomatic relief of acute diarrhoea and chronic diarrhoea (for example in adults with irritable bowel syndrome), and to reduce stool frequency in ileostomy.

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 • take only on an empty stomach (1 hour before or 2 hours after a meal) • take with a full (8 oz.) glass of water • find right dose on chart below. If possible, use weight to dose; otherwise, use age. adults and children 12 years and over 2 tablets after the first loose stool; 1 tablet after each subsequent loose stool; but no more than 4 tablets in 24 hours children 9-11 years (60-95 lbs) 1 tablet after the first loose stool; 1/2 tablet after each subsequent loose stool; but no more than 3 tablets in 24 hours children 6-8 years (48-59 lbs) 1 tablet after the first loose stool; 1/2 tablet after each …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-04-05. 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 a peripheral opioid-receptor agonist acting on the gut wall; it slows intestinal motility and increases transit time without normally crossing into the central nervous system at therapeutic doses.

Prescribing in practice

  • Do not use in acute ulcerative colitis, bloody or inflammatory diarrhoea, or suspected infective (e.g. invasive bacterial) diarrhoea, because inhibiting motility risks toxic megacolon.
  • Serious cardiac effects, including QT prolongation and arrhythmia, have been reported with abuse or overdose at very high doses (MHRA warning).
  • Not suitable for young children; check the licensed lower age limit before recommending.

Monitoring

Mainly a clinical assessment: review response, hydration and stool frequency, and reassess if diarrhoea persists, worsens, or is accompanied by fever or blood.

Counselling the patient

  • Stop and seek medical advice if you develop a fever, see blood in your stools, or your symptoms do not settle within a couple of days.
  • Keep drinking fluids to replace what you lose.
  • Never take more than the recommended amount — very high doses can cause dangerous heart rhythm problems.

Evidence & guidelines

Established symptomatic therapy; MHRA Drug Safety Update highlights cardiac risks with high-dose misuse.

Reference: MHRA Drug Safety Update 2018 (Loperamide); 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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