Aspirin (Acetylsalicylic Acid) Poisoning in Cats

Aspirin toxicity in cats at a glance

  • About: Aspirin is a popular over the counter medication to treat pain, fever, and inflammation. While safe for humans, aspirin is toxic to cats.
  • Toxic effects: Bone marrow suppression, liver inflammation, bleeding, stomach ulceration, and kidney damage.
  • Symptoms: Vomiting blood, black and tarry feces, loss of appetite, rapid breathing, and jaundice.
  • Treatment: Gastric decontamination, fluid therapy to correct dehydration and electrolyte imbalances and antacids.

Aspirin (acetylsalicylic acid) is a popular over the counter non-steroidal anti-inflammatory drug (NSAID) used to treat fever (antipyretic), reduce inflammation, thin the blood (by preventing the formation of blood clots) and relieve mild pain (analgesic).

Unfortunately, aspirin is also one of the most common causes of poisoning in cats. Unlike humans, cats metabolise aspirin very slowly, and it is extremely easy to give a cat a fatal overdose in as little as a single tablet. Aspirin poisoning can occur in cats of all ages; however, kittens and senior cats are at increased risk.

Why is aspirin so toxic to cats?

UDP-glucuronosyltransferase 1-6 (UGT1A6) is an enzyme produced by the liver and encoded by a gene of the same name. UGT1A6 evolved to help detoxify plant-based toxins (phytoalexins) by a process called glucuronidation.

As cats evolved, mutations occurred on this gene to the point where it only produces a minute amount of UGT1A6 compared to other animals and people. As a cat’s diet is primarily carnivorous, it did not need UGT1A6 to help it detoxify plant-based toxins. Mutations of this gene had no impact on the survival of the cat species. One study lead by Michael Court in 1997 found 18 species of cat, from cheetahs to lions lacked this enzyme, which suggests that the mutations occurred in a common ancestor.

Cats also lack N-acetyltransferase 2, an enzyme in humans encoded in the NA2 gene, N-acetyltransferase 2 detoxifies certain drugs and metabolites.

This means that it takes considerably longer for the body to metabolise aspirin than it would in a human or dog. The biological half-life of aspirin in cats is approximately 40 hours compared to 7.5 hours in dogs.

How does aspirin poisoning occur?

  • Intentional administration of high doses of aspirin.
  • Administration of low doses of aspirin over a prolonged period, because cats are not able to metabolise the drug as quickly as other animals, levels quickly build up, resulting in toxicity.
  • When a pet owner accidentally gives a product containing aspirin such as Pepto-Bismol.
  • Accidental ingestion, such as eating an aspirin dropped on the floor. This is more likely to occur in dogs than cats who tend to be fussier about what they eat.
  • Deliberate poisoning.


Aspirin overdose causes inflammation, bleeding, ulceration, perforation of the stomach, bone marrow toxicity, metabolic acidosis and damage to the kidneys and liver.

Symptoms develop within 3-6 hours of ingestion but can be slower to occur if lower doses are given over a prolonged period. The first signs of aspirin toxicity include loss of appetite and vomiting. As multiple body systems are affected, symptoms can be varied and include the following.

Gastrointestinal disturbances:

Gastrointestinal disturbances are usually the first symptoms to appear; aspirin irritates the gastric mucosa. Symptoms include:

Respiratory centre stimulation:

Aspirin stimulates the respiratory centre (located in the brain):

  • Rapid breathing (tachypnea)
  • Hyperthermia (elevated body temperature)
  • Respiratory alkalosis (increased respiration elevates the blood pH)

Acute kidney failure:

  • Vomiting
  • Loss of appetite
  • Increased thirst
  • Diarrhea

Liver failure:

  • Jaundice (yellowing of the gums and mucous membranes)


  • Nervous system disorders including hyperexcitability, loss of balance (ataxia), depression, and seizures.
  • Aspirin inhibits the formation of platelets, which are required to help the body form blood clots. This can lead to spontaneous bleeding. You may notice red spots under the skin and gums, known as petechiae.
  • Bone marrow toxicity can result in anemia; symptoms may include pale gums, lethargy. Heinz body formation, hemolysis (blood cell destruction) and thrombocytopenia (low platelet count) may also be present.
  • Increased respiration and urination due to metabolic acidosis and acute kidney failure can result in dehydration and electrolyte imbalances.


Diagnosis is based on a history of exposure to the drug; however, in the case of deliberate poisoning, the pet owner may not be aware that the cat has ingested aspirin.

Diagnostic workup:

  • Complete blood count: A blood test that measures the cellular components of the blood (red blood cells, white blood cells and platelets. CBC may reveal anemia, Heinz bodies, and thrombocytopenia.
  • Biochemical profile: A test on the clear/fluid portion of the blood, the biochemical profile measures a number of chemicals and enzymes which provides important information on kidney and liver function and electrolytes.
  • Urinalysis: The urine sample is evaluated for its physical properties which include specific gravity, colour and clarity, and biochemically for pH, protein, glucose, and bilirubin. The urinalysis can help the veterinarian determine how concentrated the urine is, which can help to evaluate kidney function.
  • Blood gas test: To monitor respiratory gas alkalosis or anion-gap metabolic acidosis as toxicity progresses. A small amount of blood is drawn from an arterial blood supply and placed in a blood gas analyser.


Prompt diagnosis and treatment are vital if your cat is to recover from aspirin poisoning. There is no antidote; the goal of treatment is to remove the drug from the body and offer supportive care.

Emergency care:

  • Ventilate the cat if it is experiencing breathing difficulty
  • Provide supplementary oxygen where necessary
  • Administer medications to control seizures
  • Re-establish hydration and electrolyte balance with the administration of intravenous fluids. This also helps the kidneys to flush the toxin out of the body via the urine (known as diuresis). Furosemide may be administered to enhance this.
  • Maintain normal body temperature if the cat has become hyperthermic via external cooling such as fans.


  • Induce vomiting if the exposure was recent (within the past 2-4 hours) or gastric lavage (stomach pumping), followed by administration of activated charcoal to prevent further absorption.
  • Hemodialysis is a procedure where a dialysis machine and a special filter (artificial kidney) are used to remove wastes from the blood which would ordinarily be performed by the kidneys.


  • Sodium bicarbonate will be administered intravenously to correct metabolic acidosis and alkalinise the urine, treatment with sodium bicarbonate can lead to hypokalemia (potassium deficiency) and therefore should be administered carefully with frequent monitoring of urine or blood pH.
  • Medications such as sucralfate and misoprostol are medications used to protect the gastrointestinal tract and treat or prevent stomach ulcers by reducing the amount of stomach acid produced, or by forming a barrier over the ulcers.


The prognosis is favourable if treatment commences before the onset of symptoms; otherwise, it is poor.


  • Never administer medications to your cat unless prescribed by a veterinarian.
  • Always follow your veterinarian’s directions to the letter.
  • Have one member of the household responsible for administering medication so that your cat isn’t accidentally medicated twice.
  • Keep all medications away from cats and children.
  • Don’t store human and pet medications together.
  • If you suspect your cat has had aspirin, take him to the veterinarian immediately.


Aspirin can be used in very small doses to prevent blood clots, reduce fever and relieve pain but only under strict veterinary supervision. Cat owners mustn’t self-medicate their cat, particularly aspirin because this will most likely have lethal consequences for the cat.

The safe dose for cats is 10mg/kg every 48 hours. Use with caution in cats with liver or kidney disease, gastric ulcers, coagulation disorders, asthma, pregnancy, in kittens or senior cats.

Stop blood thinners (including aspirin) 1-2 weeks before surgery.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio