Home/Medicines/Naltrexone

Naltrexone

Prescription

Opioid Antagonist

Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

2 available

Interactions

3 documented

Formulations

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

Frequency

q12–24h

🐈

Cat

Psychogenic alopecia and compulsive grooming

Dose

0.5–2 mg/kg

Route

Frequency

q12–24h

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 →

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

Educational reference only

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.

Educational reference only

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.

Educational reference only

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

Plumb's Veterinary Drug Handbook
Withrow & MacEwen's Small Animal Clinical Oncology
Merck Veterinary Manual
NRC Nutrient Requirements of Dogs and Cats
Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

ASPCA Animal Poison Control Center Guidelines
AAHA Diabetes Management Guidelines
ASPCA Poison Control Guidelines
RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

EPIC Study (J Vet Intern Med 2016)
JVIM FAT CAT Study

Regulatory & approvals — 1

CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

Washington State University VCPL MDR1 Database

Related medicines

Other medicines in the same class (Opioid Antagonist).

Naloxone

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

dogcat