Morphine

What is this medication for?

• Acute pain, drowsiness, anesthetic adjunct, cardiogenic pulmonary edema (adjunct)
• Antitussive, antidiarrheal (hypermotile diarrhea)
• Analgesic (with sedative cover — see excitation warning); epidural analgesia
• Analgesia/epidural per protocols

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Histamine release (with rapid into a vein) → low blood pressure, bronchoconstriction (Notable with into a vein bolus)
• Defecation after initial dose (Common, transient)
• Hyperthermia (Reported)
• Hypothermia (Reported)
• Excitement/CNS stimulation (Common at effective analgesic doses)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Hypersensitivity; concurrent MAOIs; toxin-induced diarrhea (until cleared); scorpion envenomation (Centruroides spp.)
• has or has had: Head injury/↑ICP, acute abdomen, respiratory disease, acute uremia (affects ADH); give into a vein slowly to avoid low blood pressure

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • MAO inhibitors (amitraz, selegiline)
  • Other CNS depressants
  • Tricyclic antidepressants
  • Diuretics

Storage and handling

Room temperature, protect from light/freezing. More stable at pH <4 — high-pH admixture causes darkening (oxidation). Schedule II. Repackaged syringes stable 70 days; epidural admixture with saline stable 14 weeks.

Good to know

• Give into a vein doses slowly — rapid into a vein push causes histamine release and significant low blood pressure.
• Common combo protocols: MMK (morphine + medetomidine/dexmedetomidine + ketamine) for short procedures; MLK (morphine + lidocaine + ketamine) CRI for perioperative analgesia.
• Horses commonly need pre-treatment with an alpha-2 agonist or acepromazine to blunt morphine-induced excitement.