Can Cats Eat Onions?

Cats cannot eat onions (Allium cepa) or any other members of the Allium family. Allium spp., which includes onion, garlic, chives and leeks contain sulfur-containing oxidants (thiosulfinates and thiosulfonates). Sulfur-containing oxidants are metabolised into reactive oxidants which can lead to Heinz body hemolytic anemia.

Heinz bodies are abnormal structures that form as a result of the denaturation of hemoglobin, which is the protein that carries oxygen in red blood cells. Normally, hemoglobin is tightly folded and structured, but when exposed to sulfur-containing oxidants, becomes denatured and forms a clump, which is called a Heinz body. Heinz bodies appear as small, round or irregularly shaped inclusions within the red blood cell when viewed under a microscope. The presence of Heinz bodies can interfere with the normal function of red blood cells, such as oxygen transport, and may cause the cells to become more fragile and prone to hemolysis (rupture).

Heinz body hemolytic anemia

Garlic is the most toxic member of the Allium family, however, all Allium species are toxic to cats. Products that contain garlic, onion, onion flakes, powder and salt are also toxic. Most cats will not consume onion on its own due to its strong smell. Exposure may occur when a caregiver feeds the cat a product that contains onion or garlic such as baby food which is often given to sick cats.

Clinical signs

  • Pale mucous membranes: The gums, inner eyelids, and other mucous membranes may appear pale due to the decreased number of red blood cells.
  • Weakness or lethargy: The reduced number of red blood cells and subsequent decrease in oxygen delivery to tissues can cause weakness and lethargy.
  • Panting (tachypnea): As red blood cell levels drop, the lungs compensate by attempting to bring in more oxygen.
  • Jaundice: As red blood cells break down, they release a pigment called bilirubin, which can build up and cause yellowing of the skin and whites of the eyes.
  • Increased heart and respiratory rates: In an attempt to compensate for the decreased oxygen-carrying capacity of the blood, the heart and respiratory rates may increase.
  • Dark urine: As bilirubin is excreted in the urine, it can cause the urine to appear dark or brown.
  • Gastrointestinal disturbances: Abdominal pain, loss of appetite, drooling, diarrhea, and vomiting.

It can take several days for clinical signs to develop as red blood cells are lost faster than the body can replace them. Not all cats with Heinz body anemia will exhibit all of these clinical signs, and the severity of the signs may vary depending on the extent of the anemia. If you suspect your dog cat has ingested onion or garlic, seek immediate veterinary care.


The veterinarian will perform a complete physical examination and obtain a medical history. This will include how long symptoms have been present, recent food the cat has eaten, and if the cat has been administered any prescription or non-prescription medications.

A diagnostic workup will be necessary to check the blood cell count and evaluate organ function.

Diagnostic workup:

  • Baseline tests: Biochemical profile to evaluate organ function, complete blood count and urinalysis. CBC may reveal a reduced number of red blood cells.
  • Blood smear: A drop of blood is spread over a glass slide and examined under a microscope to evaluate at the size and shape of red blood cells and look for the presence of Heinz bodies. Note: Cats can have Heinz bodies in their red blood cells without having anemia.


If ingestion was recent, the veterinarian will induce vomiting, followed by activated charcoal to bind to any remaining toxins. Unfortunately, most cats do not develop clinical signs for several days post-exposure.

A blood transfusion will be necessary for cats with severe anemia. The donor cat’s blood group must be the same as the recipient’s. Most veterinary practices have a resident practice cat who may be able to donate.

Oxygen therapy can be administered to compensate for reduced circulating oxygen levels.

Intravenous fluids to treat or prevent dehydration and protect the kidneys.

What to do if your cat eats onion

If your cat eats onion or a product with onion or other Allium species, contact your veterinarian immediately. Prompt medical treatment will provide a better outcome as the veterinarian can decontaminate the gastrointestinal tract to prevent absorption. Once the onion has been digested, the only treatment is supportive.

How much onion is toxic to cats?

Consumption of 5 grams per kilo is enough to induce clinical changes to the blood. Obviously the more onion the cat consumes, the greater the risk. But cats should not eat any food which contains onion, even the tiniest amount of onion can be deadly. The image below shows just how little 5 grams of onion is. This was one slice of a tiny onion the size of a plum.



Cats are not small humans and many foods and medications that are safe for us can be deadly to cats.

  • Do not feed cats any food which contains onion, garlic, leek or chives. There is no safe limit, and even a small exposure can be fatal.
  • Always read product labels. Even foods that appear harmless such as baby food and seasoning can contain onion, garlic or their by-products.
  • Never leave food unattended on benchtops or tables.
  • For anorectic cats, tinned tuna or steamed chicken breast are safer options than baby food which often contains onion and garlic.
  • Always check with your veterinarian before giving cats any type of supplement or over-the-counter medication.
  • If you grow onion, garlic, chives or leeks in the garden, cover with bird safe netting to keep cats away.

If your cat does consume onion or garlic, seek immediate veterinary care.


  • 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

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