Can cats eat onions?

Is onion toxic to cats?

Yes. Onion is poisonous to cats in every form the sources name. The Merck Veterinary Manual describes cats as the most susceptible species, ahead of dogs, and Pet Poison Helpline states that onion and the other alliums are poisonous to dogs, cats and livestock. None of the sources on this page names a safe form.

Onion contains sulfur-containing oxidants, which Merck thinks are responsible for the hemolysis that follows ingestion; the ASPCA names N-propyl disulfide as the toxic principle. Once absorbed, they cause oxidative damage to red blood cells, Heinz body formation and methemoglobinemia. The result is hemolytic anemia, the breakdown of red blood cells. Spring onions and scallions belong to the same family and count the same way.

How much onion is toxic to cats?

Very little. Merck reports poisoning in cats after less than a teaspoon of cooked onions, or 5 g/kg of raw onions. Those are the only cat-specific amounts in the sources used here, and none of them describes any amount as safe, so a cat that has eaten any onion needs a call to a vet.

These amounts are reports of cats that were poisoned, not a safe limit. Merck's figures for dogs are different and are not used on this page, because Merck ranks cats as the more susceptible species.

Can cats eat cooked onions?

No. Cooked onion has poisoned cats: one of Merck's two cat figures is for cooked onion, less than a teaspoon of it, and Merck's key points list raw, cooked and concentrated forms together as able to cause Heinz body hemolytic anemia. Cooking is one of the ways the harmful compounds are released from the plant.

Are garlic, chives and leeks toxic to cats too?

Yes. Garlic, chives and leeks belong to the same Allium family as onion, and Pet Poison Helpline states that all of them are poisonous to dogs, cats and livestock. Merck covers onion and garlic as a single toxicosis with the same mechanism, and rates garlic as the more toxic of the two.

A dish that avoids onion but is built on garlic is not a safer choice. Our list of checked foods shows the rating and sources for garlic and every other food we have reviewed.

What are the symptoms of onion poisoning in cats?

Vomiting, lethargy or weakness, pale or yellow gums, a rapid heart rate and breathing, and red or brown-tinged urine are the signs the sources describe. In severe cases a cat can collapse. The signs of the anemia typically appear several days after the onion was eaten, not on the same day.

Vomiting may occur sooner, but hemolytic anemia takes 3–5 days to develop, so a cat can look completely normal on the first day. That gap is the reason the advice above is to call straight away rather than wait for signs. By the time weakness or pale gums appear, the anemia is already established.

Where does onion hide in food?

Merck links poisoning most often to concentrated forms: dehydrated onion flakes, onion powder and dry onion soup mixes. Onion powder, dehydrated flakes, cooked onion, and green onion or scallion all count as onion, so check the ingredient list of any seasoned or ready-made food before sharing it with your cat — flavored canned tuna included.

The ingredient list matters more than whether onion is visible in the dish. Onion is not the only everyday food rated toxic here: grapes and raisins are too.

What is the treatment for onion poisoning in cats?

Merck describes treatment as early decontamination of the gut when the ingestion is recent, followed by management of the anemia. A vet will likely want blood work (a CBC) to check for Heinz bodies and anemia. Do not try to make your cat vomit at home; leave decontamination to your vet.