ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Antidiarrhoeal (Opioid Receptor Agonist — Peripheral) Pregnancy: Caution — limited data; avoid in first trimester; use in later pregnancy only if clearly needed.

Loperamide Hydrochloride

Brand names: Imodium, Arret

Adult dose

Dose: Acute diarrhoea: initially 4mg, then 2mg after each loose stool. Chronic diarrhoea: 4–8mg/day in divided doses, adjusted to response.
Route: Oral (capsules, tablets, or liquid)
Frequency: After each loose stool (acute); regular divided doses (chronic)
Max: 16mg/day
For acute diarrhoea: do not use >48 hours without medical assessment. Do not use in bloody diarrhoea or suspected infectious colitis (bowel perforation risk from delayed transit). For ileostomy: highly effective for high-output stoma — doses up to 16mg/day used regularly.

Paediatric dose

Route: Oral
Frequency: After each loose stool or 2–4 times daily
Max: 2mg per dose
Licensed for acute diarrhoea ≥12 years only (MHRA restriction). Off-label (BNFC) for chronic diarrhoea: ≥4 years — 100–200 micrograms/kg (max 2mg) 2–4 times daily under specialist supervision only. Not for acute infectious diarrhoea in children. Source: BNF for Children 2024.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Use with caution in hepatic impairment — increased systemic exposure may cause CNS toxicity.

Clinical pearls

  • Acts on enteric μ-opioid receptors — reduces gut motility and secretion without significant CNS penetration at therapeutic doses.
  • MHRA 2018: loperamide misuse at high doses causes serious cardiac arrhythmias (QT prolongation, ventricular tachycardia). Never exceed 16mg/day.
  • Ileostomy high-output: loperamide is highly effective — take 30 min before meals and at night. Doses up to 16mg/day routinely used in specialist settings.
  • Do not use in antibiotic-associated or infective colitis — prolongs carrier state and may worsen outcomes.

Contraindications

  • Acute bloody diarrhoea or dysentery
  • Acute ulcerative colitis (risk of toxic megacolon)
  • Antibiotic-associated colitis (Clostridioides difficile — do not use antimotility agents)
  • Acute surgical abdomen

Side effects

  • Constipation (most common — dose-dependent)
  • Abdominal cramping, bloating
  • Nausea
  • Toxic megacolon (if used in active colitis — rare but life-threatening)
  • CNS effects (dizziness, drowsiness) at high doses or in hepatic impairment

Interactions

  • QT-prolonging drugs: loperamide at high doses may prolong QT (caution)
  • P-glycoprotein inhibitors (quinidine, ritonavir): increase loperamide CNS penetration — CNS toxicity at standard doses

Monitoring

  • Stool frequency and consistency
  • Hydration status
  • Signs of toxic megacolon (fever, abdominal distension)

Reference: BNFc; BNF 90; MHRA Drug Safety Update 2018 (Loperamide); SPC Imodium. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways