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Morphine Sulfate

Opioid Analgesic (Full Agonist)

Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

3 available

Interactions

7 documented

Formulations

Mechanism of action

Prototype full mu-opioid receptor agonist providing potent analgesia, sedation, and euphoria. Metabolized to active morphine-6-glucuronide (analgesic) and morphine-3-glucuronide (neuroexcitatory, poorly analgesic). Variable histamine release on IV bolus.

At a glance

Class

Opioid Analgesic (Full Agonist)

Schedule

Controlled Substance

Storage

Store at room temperature, protect from light; controlled substance secure storage required

Dosing

🐕

Dog

Standard full opioid for moderate-severe pain

Dose

0.1–0.5 mg/kg

Route

IV (slowly), IM, SQ, Epidural

Frequency

q2–4h (intermittent); continuous (CRI)

🐈

Cat

Effective in cats

Dose

0.1–0.2 mg/kg

Route

IM, SQ, Epidural, IV (with caution)

Frequency

q3–4h (intermittent); continuous (CRI)

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 — 4

Strength

—

Strength

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Strength

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Strength

—

Storage

Store at room temperature, protect from light; controlled substance secure storage required

Safety

Monitoring parameters

Respiratory rateSpO2Pain scoresBlood pressureLevel of sedationGI motility

Educational reference only

Interactions

Major — 2

Buprenorphine

major

Buprenorphine is a partial mu-agonist with very high receptor binding affinity. It occupies mu-receptors and prevents full agonists from achieving full analgesic potential.

Management: Do not combine. Allow 4-6h for buprenorphine dissociation before giving full mu-agonist. If rescue needed on buprenorphine, use non-opioid (NSAID, ketamine CRI).

Naltrexone

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.

Moderate — 5

Maropitant

moderate

Maropitant inhibits CYP enzymes that metabolize some opioids, potentially increasing opioid plasma levels. Also synergistic antiemetic effect (desired).

Management: Antiemetic co-administration is standard practice. Monitor for increased sedation. Clinical significance of PK interaction is modest.

Dexmedetomidine

moderate

Synergistic sedation and analgesia. Dexmedetomidine reduces opioid MAC-sparing by additional 40-60%. Additive bradycardia.

Management: Intended combination — reduce opioid dose by 30-50%. Monitor heart rate. Profound bradycardia may require glycopyrrolate.

Metoclopramide

moderate

Opioids slow GI motility (anti-prokinetic). Metoclopramide stimulates GI motility (prokinetic). Pharmacologically opposing effects.

Management: Metoclopramide antiemetic effect (D2 blockade) is preserved, but prokinetic effect is reduced by concurrent opioids. For prokinetic benefit, may need higher metoclopramide dose.

Diazepam

moderate

Additive CNS and respiratory depression via different mechanisms (mu-opioid vs GABA-A).

Management: Monitor respiratory rate and SpO2. Reduce opioid dose when adding benzodiazepine.

Medetomidine

moderate

Synergistic sedation and analgesia. Additive bradycardia. Standard premedication combination at reduced doses.

Management: Intended combination. Reduce individual doses by 30-50%. Monitor heart rate. Reverse medetomidine with atipamezole when appropriate.

Educational reference only

Brands

Other markets

Morphine Sulfate

MS Contin

AVINZA

FAQs

Frequently asked questions

›What is Morphine Sulfate?

Morphine Sulfate is a opioid analgesic (full agonist) used in pets. Prototype full mu-opioid receptor agonist providing potent analgesia, sedation, and euphoria. Metabolized to active morphine-6-glucuronide (analgesic) and morphine-3-glucuronide (neuroexcitatory, poorly analgesic). Variable histamine release on IV bolus.

›What is Morphine Sulfate used for in pets?

Morphine Sulfate is used in veterinary medicine for: Standard full opioid for moderate-severe pain; Effective in cats.

›What is the Morphine Sulfate dose for dogs?

For dogs, Morphine Sulfate is typically dosed as follows — Standard full opioid for moderate-severe pain: 0.1–0.5 mg/kg IV (slowly)/IM/SQ/Epidural q2–4h (intermittent); continuous (CRI). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What is the Morphine Sulfate dose for cats?

For cats, Morphine Sulfate is typically dosed as follows — Effective in cats: 0.1–0.2 mg/kg IM/SQ/Epidural/IV (with caution) q3–4h (intermittent); continuous (CRI). Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›Does Morphine Sulfate need a prescription?

Morphine Sulfate is available over the counter. Even so, you should consult your veterinarian before giving any medication to your pet.

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 Analgesic).

Meperidine (Pethidine)

Synthetic mu-opioid receptor agonist approximately 1/10th the potency of morphine. Also has local anesthetic properties (sodium channel blockade) and anticholinergic effects. No histamine release (unlike morphine). Short duration (1–2h).

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