Loperamide
Loperamide hydrochloride
Also known as: Imodium A-D · Neo-Diaral · K-Pek II · Diah-Limit · Diarolaeze · Entrocalm · Norimode · PJ 185 · R 18553 · Loperamida · Loperamidum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Antidiarrheal | 0.08 mg/kg | PO | three times daily | — | 🌎 NA |
| Antidiarrheal | 0.1-0.2 mg/kg | PO | q8-12h | — | 🌎 NA |
| Antidiarrheal | 0.1 mg/kg | PO | three times a day | Maximum 5 days | 🌎 NA |
| Adjunctive treatment for diarrhea associated with chemotherapy | 0.08 mg/kg | PO | three times daily | — | 🌎 NA |
| Antidiarrheal | 0.08 mg/kg | PO | 3-4 times a day | — | 🌎 NA |
| Antidiarrheal | 0.1-0.2 mg/kg | PO | q6-12h | — | 🌎 NA |
| Management of non-specific acute and chronic diarrhoea, and irritable bowel syndrome | 0.04-0.2 mg/kg | PO | q8-12h | As needed | 🌍 EU |
- Antidiarrheal: Collies and related breeds (MDR1 mutation) may be overly sensitive
- Antidiarrheal: Potentially contraindicated when diarrhea is suspected to be caused by enteric infections
- Management of non-specific acute and chronic diarrhoea, and irritable bowel syndrome: Do not use in dogs likely to be ivermectin-sensitive (e.g., collies) due to MDR1 mutation risk.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Diarrhea | 0.04-0.06 mg/kg | PO | twice daily | — | 🌎 NA |
| Diarrhea | 0.08-0.16 mg/kg | PO | q12h | — | 🌎 NA |
| Management of non-specific acute and chronic diarrhoea, and irritable bowel syndrome | 0.04-0.2 mg/kg | PO | q8-12h | As needed | 🌍 EU |
- Diarrhea: Using the suspension. Use is controversial; may react with excitatory behavior.
- Diarrhea: Use is controversial.
- Management of non-specific acute and chronic diarrhoea, and irritable bowel syndrome: Use with care; excitability may be seen.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Antidiarrheal (Rabbits) | 0.1 mg/kg in 1 mL of water | PO | q8h for 3 days, then once daily for 2 days | 5 days total | 🌎 NA |
| Antidiarrheal (Mice, Rats, Gerbils, Hamsters, Guinea pigs, Chinchillas) | 0.1 mg/kg in 1 mL of water | PO | q8h for 3 days, then once daily for 2 days | 5 days total | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Loperamide is a synthetic, peripherally acting piperidine-derivative opiate agonist primarily used as an antidiarrheal and gastrointestinal (GI) motility modifier in veterinary medicine.
Unlike many other opioids, loperamide is a substrate for the P-glycoprotein (P-gp) efflux pump at the blood-brain barrier. In normal animals, this prevents the drug from accumulating in the central nervous system (CNS), thereby minimizing typical opioid neurological effects.
Clinical Pearl: Loperamide is highly effective for symptomatic relief of non-infectious diarrhea (such as chemotherapy-induced diarrhea from drugs like toceranib). However, it must be used with extreme caution—or avoided entirely—in herding breeds (e.g., Collies, Australian Shepherds) due to the ABCB1-1Δ (MDR1) mutation. In these dogs, the defective P-gp pump allows loperamide to cross the blood-brain barrier, leading to profound and potentially fatal neurotoxicity even at standard doses.
Mechanism of action
Loperamide exerts its antidiarrheal effects through multiple mechanisms within the gastrointestinal tract:
- μ-opioid receptor agonism: Binds to mu-receptors in the myenteric plexus of the intestinal wall → inhibits the release of acetylcholine and prostaglandins → reduces peristalsis and increases intestinal transit time, allowing for greater fluid absorption.
- δ-opioid receptor agonism: Binds to delta-receptors → decreases intestinal secretion induced by cholera toxin and prostaglandins.
- Calcium channel modulation: Inhibits diarrheas caused by factors utilizing calcium as a second messenger (non-cAMP/cGMP mediated).
- Mucosal absorption: Directly enhances the mucosal absorption of water and electrolytes.
Safety & warnings
Contraindications
- Dogs tested positive for the ABCB1-1Δ (MDR1) mutation
- Untested dogs of herding breeds susceptible to the MDR1 mutation
- Diarrhea caused by toxic ingestion (until the toxin is eliminated)
- Known hypersensitivity to narcotic analgesics
- Infectious enteritis (relative contraindication, as decreased motility can delay pathogen clearance)
- Intestinal obstruction
- Dogs likely to be ivermectin-sensitive (MDR1/ABCB1 mutation, e.g., Collies, Australian Shepherds)
- Infectious enteritis (where decreased motility may delay pathogen clearance)
- Toxigenic diarrhea
Adverse effects
- Constipation
- Bloat
- Paralytic ileus
- Toxic megacolon
- Pancreatitis
- CNS depression (especially in MDR1-mutant dogs)
- Excitatory behavior (cats)
- Excitability (especially in cats)
- Profound sedation and ataxia (in MDR1 mutant dogs)
Precautions
Use with caution in patients with hypothyroidism, severe renal insufficiency, adrenocortical insufficiency (Addison's disease), and in geriatric or severely debilitated patients.
Use with extreme caution in patients with head injuries or increased intracranial pressure, as well as acute abdominal conditions (e.g., colic), as opiates may obscure the diagnosis or clinical course.
Use with extreme caution in patients suffering from respiratory disease or acute respiratory dysfunction (e.g., pulmonary edema secondary to smoke inhalation).
Use with extreme caution in patients with hepatic disease exhibiting CNS clinical signs of hepatic encephalopathy, as hepatic coma may result.
Small Patient Dosing: Many clinicians recommend avoiding tablet/capsule forms in dogs weighing less than 10 kg due to potency; dosage titration using liquid forms is recommended for safe use.
Drug interactions
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Inhibits P-glycoprotein (P-gp), which may increase loperamide plasma concentrations and risk of CNS toxicity.
Additive reduction in GI motility, increasing risk of ileus
May increase CNS penetration of loperamide, leading to neurotoxicity
Additive sedation if loperamide crosses the blood-brain barrier
Monitoring
- Clinical efficacy (resolution of diarrhea)
- Fluid and electrolyte status (especially in severe diarrhea)
- CNS effects (sedation, ataxia, depression), particularly if using high dosages or in susceptible breeds
- Fecal consistency and frequency
- Signs of constipation or paralytic ileus
- Neurological status (watch for sedation or ataxia, especially in at-risk breeds)
- Hydration status
Pharmacokinetics
Half-life
Absorption
In dogs, reportedly has a faster onset of action than diphenoxylate.
Distribution
Unknown if the drug enters milk or crosses the placenta. Excluded from the CNS in normal animals by P-glycoprotein.
Metabolism
Hepatic metabolism.
Elimination
Primarily fecal elimination.
Overdose
In dog toxicity studies, doses of 1.25-5 mg/kg/day produced vomiting, depression, severe salivation, and weight loss.
CRITICAL WARNING: Breeds with a defective MDR1 (ABCB1-1Δ) gene are profoundly more sensitive to CNS depression with loperamide than other breeds and have shown clinical signs of toxicity at doses as low as 0.06 mg/kg.
Common clinical signs of overdose include diarrhea, vomiting, lethargy, anorexia, weakness, and hypersalivation.
Treatment:
- Follow standard GI decontamination protocols.
- Avoid apomorphine for emesis, as it can have additive CNS or respiratory depressant effects.
- Naloxone may be used to treat severe CNS/respiratory depression; higher than usual doses of naloxone may be required to reverse loperamide toxicity.
Available products
Formulations
- Oral liquid
- Capsules
- Tablets
- 2 mg capsule
- 2 mg tablet
- 0.2 mg/ml syrup
Human-labeled
- Loperamide HCl Oral Liquid: 1 mg/5 mL (0.2 mg/mL) & 1 mg/7.5 mL
- Loperamide HCl Capsules and Tablets: 2 mg
- Diah-Limit
- Diarolaeze
- Entrocalm
- Imodium
- Norimode
Regulatory status
Available as POM, P, or GSL depending on pack size and specific formulation.
Classified as POM, P, or GSL depending on the product.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Loperamide capsules or oral solution should be stored at room temperature in well-closed containers. It is recommended that the oral solution not be diluted with other solvents.
Client information
Loperamide is a medication used to help control diarrhea in pets.
- Breed Warning: Do NOT use this medication in herding breeds (such as Collies, Shelties, Australian Shepherds, or mixed breeds with white feet) unless they have been specifically tested and cleared for the MDR1 gene mutation. In these dogs, loperamide can cause severe and life-threatening neurological reactions.
- Cats: Use in cats is generally not recommended unless strictly directed by your veterinarian, as it can cause unusual excitatory behavior.
- Administration: Liquid forms are often preferred for small dogs to ensure accurate dosing. Do not dilute the oral liquid with other liquids.
- When to call the vet: Contact your veterinarian immediately if the diarrhea persists for more than 48 hours, if your pet appears unusually listless, depressed, or uncoordinated, or if they develop a high fever or bloody stool.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.