As it applies to dogs, warfarin is a rarely used drug for the treatment and prevention of thrombosis. The main reason for its lack of popularity is the cost, risk of blood loss and lack of evidence supporting its benefits upon mortality. Unlike most anticoagulants, it does not act directly but instead hinders the mechanism of vitamin K1 to produce its effects. Careful monitoring during treatment is important.

Other anticoagulants such as heparin are more commonly used for the treatment of dogs though some indications are still controversial.

Typical Dosage

Note: The following dosage is only a guideline. Never give warfarin to your dog without approval from your vet.

When used in dogs the dosage typically starts at 0.1 mg/lb. This dose may be adjusted based on the time it takes for your dog’s blood to clot (also known as prothrombin time, or “PT”). The initial 0.1 mg/lb dosage is displayed on the chart below:

Chart for the canine dose of warfarin

Adjunctive administration of heparin (another anticoagulant) is sometimes practiced until the correct dosage of warfarin is established.

Example Dosage: A 20 lb dog would require 2 mg daily, which may be adjusted based on their response to the drug.

Is It Safe For Use In Dogs?

The use of this drug may lead to complications and side effects in some dogs. These complications can be severe, even life threatening, particularly when overdose amounts are ingested.

Contraindications & Drug Interactions

There are many drug interactions and contraindications associated with use of this medicine. Perhaps the most serious of which is the unapproved use of other drugs with anticoagulant effects such as aspirin, or the administration of warfarin to dogs who are prone to hemorrhage.

Pregnant/Nursing Dogs: Pregnant dogs should not be given this medicine due to the risk of damage to offspring and extreme caution should be practiced in nursing dogs.

Guidelines For Safe Use

Due to the risk of dangerous side effects, it’s extremely important that your dog is carefully monitored during treatment. You should never give the drug to your dog without talking to the vet. You should notify your vet about:

  • Any other medicines or supplements your dog is taking
  • All medical conditions your dog suffers from
  • Alternative options of treatment

If your dog’s PT (clotting time) is above or below the target the dose may be adjusted. If this time deviates too much from the safe zone corrective measures will be taken.

What Are The Uses?

The medicine is most commonly used to treat:

  • Thrombosis


What Side Effects Should I Expect?

The medicine can cause extremely serious side effects if massive blood loss (hemorrhage) occurs. Owners should be aware of these when deciding on using the drug to treat their dog:

  • Anemia
  • Hematoma
  • Nose bleed
  • Bruising
  • Blood in stools
  • Death

Other side effects related to bleeding may occur.


Symptoms of overdose may not appear until up to 48 hours following administration of the drug. Overdoses can cause severe hemorrhage and death. The overdose amount has been recorded as 0.45 mg/lb when administered for a number of consecutive days, or 2.27 mg/lb as a one off dosage. If an overdose is suspected you should immediately call your vet or the ASPCA Animal Poison Control hotline on (888) 426-4435. In cases of warfarin overdoses standard protocols will be followed which includes the administration of vitamin K1 and absorption of any remaining drug in the stomach.