By Lauren R. Forsythe, PharmD, MBA, DICVP; Kayla Hyland, DVM; Rania Gollakner, BS, DVM, MPH

Over-the-counter medications can cause serious side effects in your pet. Contact your veterinarian before using any over-the-counter medication and follow your veterinarian’s directions.

What is aspirin?

Aspirin or acetylsalicylic acid or ASA (brand names: Ecotrin®, Aspirin®, and others) is an anti-inflammatory, anti-clotting, fever-reducing, and pain controlling medication, used most for its anti-clotting effects in many pets.

Its use in cats, dogs, and small mammals to treat excessive clotting, inflammation, fever, and pain is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How is aspirin given?

  • Aspirin is given by mouth in the form of a tablet, preferably an enteric-coated tablet. 
  • Aspirin may also be compounded into a capsule to obtain the appropriate dose for your pet. 
  • Give with food.
  • If possible, aspirin should not be used one week prior to surgical procedures.

This medication should take effect within one to two hours; however, effects may not be obvious and so laboratory tests may be required to evaluate if this medication is working.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Aspirin may cause the following side effects:

  • nausea
  • decreased appetite
  • vomiting
  • intestinal irritation
  • bleeding of the gastrointestinal (GI) tract (signs include black/tarry stools; blood or “coffee grounds” in the vomit; or red, frank blood in the stool)
  • anemia or low blood protein can occur in severe bleeding cases 

In cats, aspirin may cause acidosis (too much acid in the body fluids), resulting in depression, gastrointestinal upset, abnormal breathing, fever and confusion.

This moderate-acting medication should stop working in a few days, although effects can be longer in pets with liver or kidney disease. However, the increased bleeding risk remains for approximately 7 to 10 days after the drug is stopped.

Cats are very sensitive to aspirin, so it is important to dose your cat carefully. If aspirin is dosed incorrectly, it can build up in your cat’s system and cause toxic effects because it clears from a cat’s system more slowly than from a dog’s. Kidney and liver damage can occur. Follow your veterinarian’s instructions carefully.

Are there any risk factors for this medication?

Aspirin should NOT BE USED in pets that:

  • are allergic to it
  • have bleeding ulcers
  • have bleeding disorders
  • have asthma
  • have kidney failure
  • are pregnant (except as a last resort)

Aspirin should be USED WITH CAUTION in:

  • pets with severe liver failure
  • pets with decreased kidney function
  • pets with low blood protein
  • cats
  • newborn pets

Are there any drug interactions I should be aware of?

The following medications should be used with caution and are sometimes contraindicated when given with aspirin:

  • ACE inhibitors
  • aminoglycosides
  • SSRI antidepressants
  • blood glucose lowering agents
  • calcium channel blockers
  • corticosteroids
  • furosemide
  • glucosamine
  • heparin
  • oral anticoagulants
  • hyaluronidase
  • NSAIDs
  • pentosane polysulfate sodium
  • phenobarbital 
  • spironolactone
  • tetracycline
  • urinary acidifying or alkalinizing drugs

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

  • Your veterinarian may monitor your pet to be sure that the medication is working. 
  • If needed, your veterinarian may monitor for bleeding or anemia. 
  • At home, monitor for side effects and contact your veterinarian if you see any.

How do I store aspirin?

  • Aspirin should be stored in a tight container, away from light and moisture. 
  • If the medication has a vinegar-like odor, do not use it.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions for contacting an emergency facility.

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