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Naltrexone

Prescription
Opioid Antagonist
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
2 available
Interactions
3 documented
Formulations
2

Mechanism of action

Long-acting competitive antagonist at mu, kappa, and delta opioid receptors. Unlike naloxone, naltrexone has high oral bioavailability and long half-life (10–13h). Used for opioid dependence, compulsive behaviors, and pruritus.

At a glance

Class
Opioid Antagonist
Schedule
Prescription
Storage
Store tablets at room temperature below 25°C; refrigerate extended-release injection

Dosing

🐕

Dog

Used for opioid-mediated pruritus, self-mutilation, and compulsive behaviors (ac
Dose
2–10 mg/kg
Route
PO
Frequency
q12–24h
🐈

Cat

Psychogenic alopecia and compulsive grooming
Dose
0.5–2 mg/kg
Route
PO
Frequency
q12–24h

Formulations

💊

Other — 2

Strength
—
Strength
—

Storage

Store tablets at room temperature below 25°C; refrigerate extended-release injection

Safety

Monitoring parameters

Hepatic enzymes at baseline and with prolonged useBehavioral responseEnsure opioid-free before surgical procedures

Interactions

Major — 3

Morphine Sulfate
major
Naltrexone is a long-acting competitive opioid antagonist (10-13h oral). Completely blocks morphine's analgesic, sedative, and respiratory effects.
Management: Stop naltrexone minimum 72h before anticipated opioid analgesia is needed (e.g., surgery). If emergency opioid needed while on naltrexone, much higher doses required and response is unpredictable.
Fentanyl
major
Naltrexone blocks all opioid receptor activity, rendering fentanyl ineffective.
Management: Discontinue naltrexone 72h before surgery. If emergency arises, non-opioid analgesia (NSAID, ketamine, local anesthetic) required.
Tramadol
major
Naltrexone blocks tramadol's mu-opioid component of analgesia. Tramadol's serotonergic component may be partially preserved but overall analgesic efficacy greatly reduced.
Management: Tramadol will be largely ineffective while on naltrexone.

Brands

Other markets

Revia
Vivitrol

FAQs

Frequently asked questions

›What is Naltrexone?
Naltrexone is a opioid antagonist used in pets. Long-acting competitive antagonist at mu, kappa, and delta opioid receptors. Unlike naloxone, naltrexone has high oral bioavailability and long half-life (10–13h). Used for opioid dependence, compulsive behaviors, and pruritus.
›What is Naltrexone used for in pets?
Naltrexone is used in veterinary medicine for: Used for opioid-mediated pruritus, self-mutilation, and compulsive behaviors (ac; Psychogenic alopecia and compulsive grooming.
›What is the Naltrexone dose for dogs?
For dogs, Naltrexone is typically dosed as follows — Used for opioid-mediated pruritus, self-mutilation, and compulsive behaviors (ac: 2–10 mg/kg PO q12–24h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Naltrexone dose for cats?
For cats, Naltrexone is typically dosed as follows — Psychogenic alopecia and compulsive grooming: 0.5–2 mg/kg PO q12–24h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Naltrexone need a prescription?
Yes. Naltrexone is a prescription medication and should only be administered under veterinary supervision.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Related medicines

Other medicines in the same class (Opioid Antagonist).

Naloxone
Rx
Competitively binds all opioid receptor subtypes (mu, kappa, delta) with highest affinity for mu receptors, rapidly displacing opioid agonists and reversing their effects
dogcat