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Can Cats Eat Onions?

Updated: August 11, 2022 by Kristen Chapple

Can Cats Eat Onions?

This has become an everyday food for us since we use it in so many of our dishes but as delicious as it is we sometimes have problems after eating too many onions. They are toxic to dogs and horses so you might ask yourself “can cats eat onions?” Let us find out!

Nutritional Value

Like garlic, onions are members of the Allium family and they are both rich in sulfur-containing compounds that are the reason for the typical smell. For humans they have anti-inflammatory effects, help our cardiovascular system, our bones and connective tissue and even help us against cancer.

Cats, on the other hand, will not find their aroma to be too exciting and the ASPCA considers onions to be toxic for them.

Side Effects

If a cat eats onions they can have quite a wide range of negative effects such as gastrointestinal upset, vomiting, the breakdown of red blood cells leading to anemia, weakness, panting and blood can come up in their urine. If they eat a high quantity these can even cause death so if you know that this has happened then you should see a veterinarian as soon as possible. Even if you don’t see any of the symptoms it is still a good idea to at least call a vet and see what their opinion is.


The substances that are toxic to animals such as dogs or cats are thiosulphate and glutathione. It was measured that if a cat eats an amount of onions equal to two grams per pound of body weight they will suffer hematologic changes and as little as 0.5% of their body weight is enough to get them intoxicated.

If the onion has only made contact with the cat’s skin then a proper wash should prevent any harm but if they ate some of it then it might be important to make your cat throw up as the anemia even a small quantity causes isn’t something you would want for your pet. Some solution of 3% hydrogen peroxide diluted in water should help induce vomiting and if your vet is too far away then this might be the best quick answer.

Forms or Varieties

Pay attention that other root vegetables like scallions, chives, leeks or garlic are just as harmful and thus all of these should be kept away from your cat. They usually wouldn’t try to eat these of their own accord but since the damage can be fatal it is better to take all the precautions you can.

We use onion in the form of fresh leaves, chopped bulb, powder for seasoning and any of these forms are just as toxic for cats.

Short Answer:

Cats should never eat onions because they can cause severe damage that can even be fatal to them.

View other toxic foods here.

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