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Can Cats Be Poisoned by Onions?

Laura García Ortiz
By Laura García Ortiz, Veterinarian specialized in feline medicine. Updated: April 13, 2022
Can Cats Be Poisoned by Onions?

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There are a number of tasty human foods that can make your cat very ill. Any food that is not designed for cats can affect the digestive system, resulting in vomiting, diarrhea, or loss of appetite. Some foods are more dangerous than others and the severity depends on how much a cat ingests of a particular food. Examples include grapes, raisins, chocolate, citrus fruits, the bones of some seeds, garlic and onions. Onion is one of the most toxic foods for cats because it contains substances that react with and destroy red blood cells, resulting in hemolytic anemia.

This AnimalWised article will explain why onions are toxic to cats, what the toxic compounds are, and what to do if your cat eats onions.

You may also be interested in: Can Dogs Eat Leek?
  1. Are onions toxic to cats?
  2. How much onion can a cat eat?
  3. Symptoms of onion poisoning
  4. What to do if my cat eats onion?

Are onions toxic to cats?

Yes, onions are poisonous to cats. The onion (Allium cepa) is a biennial herbaceous plant in the genus Allium and the family Amaryllidaceae. Other vegetables, such as garlic, leeks and chives, also belong to this family. Native to Pakistan and Iran, the plant was discovered by the Sumerians 6000 years ago.

The onion is a low-calorie vegetable, rich in fiber and contains a lot of calcium, potassium, and vitamins. It contains a lot of quercetin, an antioxidant that is characterized by its strong antioxidant properties. In addition, it contains certain substances that are harmful to cats, namely disulfide alkaloids. These substances attack the red blood cells of cats in the following way:

  • They inhibit the enzyme glucose-6-phosphate dehydrogenase, which prevents oxidation of red blood cells.
  • Heinz bodies form when the antioxidant defenses of red blood cells are destroyed.
  • Heinz bodies lead to hemolytic anemia (anemia due to the rupture or destruction of red blood cells).

If you wish to learn more about foods poisonous to cats, then read this article on poisoning in cats and what to do.

How much onion can a cat eat?

Even a small piece of onion is too much for our cats, because only 5 grams per kilogram is enough to oxidize the red blood cells. This process leads to a decrease in the hematocrit (percentage of red blood cells in the total blood) of our cats and causes clinical signs that can endanger their lives.

In general, it is important to remember that smaller cats or those that weigh less have a higher risk of poisoning than a large, heavier cat, but this is by no means a reason to offer them onions.

Also, it does not matter if the onions are given cooked or raw. These alkaloids are not denatured or inactivated by cooking. Therefore, we should never give cats onions or any other food that contains onions.

For more information on other types of fruits and vegetables cats should not consume, read this article on forbidden fruits and vegetables for cats.

Can Cats Be Poisoned by Onions? - How much onion can a cat eat?

Symptoms of onion poisoning

The symptoms produced by onion poisoning in cats are those of anemia due to a reduction in the number of red blood cells or hemolytic anemia due to their destruction. The reduction in the number of red blood cells weakens our cats, since they are responsible for the transfer of oxygen through hemoglobin. Therefore, clinical signs such as the following may occur:

  • Increased heart rate or tachycardia.
  • Increased respiratory rate or tachypnea.
  • Soft spot.
  • Lethargy.
  • Difficulty breathing or dyspnea Exercise intolerance.
  • Pale or yellowish mucous membranes (jaundice).
  • Dark colored urine.

In addition, the consumption of onions in cats may also cause digestive symptoms such as:

  • Loss of appetite or anorexia Vomiting.
  • Diarrhea.
  • Pain in the abdomen.

Find out more about other symptoms your cat may be experiencing that mean it is not healthy by reading this article how to know if my cat is sick.

Can Cats Be Poisoned by Onions? - Symptoms of onion poisoning

What to do if my cat eats onion?

If your cat has swallowed onions, you need to act quickly. Although the poisoning will not show clinical signs for some time, your cat's body is already beginning to destroy the red blood cells. Therefore, do not trust yourself and go to your veterinarian right away. Performing gastric emptying and inducing vomiting are crucial, as well as using substances that absorb or neutralize toxic substances, such as activated charcoal.

If the cat is taken to the vet too late, when the symptoms of poisoning have already appeared, blood and urine tests are necessary to determine the severity of the poisoning. Blood transfusions are also sometimes required, as well as fluid therapy and treatment for digestive symptoms if present.

Although onions are forbidden for cats, there are other fruits and vegetables that are beneficial to your cat's health. Find out more here recommended fruits and vegetables for cats.

If you want to read similar articles to Can Cats Be Poisoned by Onions?, we recommend you visit our Homemade diets category.

  • MI San Andres, R. Jurado, E. Ballesteros. (2000). Animal toxicology originating from plants. Complutense Publisher.
  • Escalona, C. Augusto, Y. Martínez. Veterinary toxicology. Available at: https://www.researchgate.net/profile/Yordan-Martinez/publication/318323199_Toxicologia_Veterinaria/links/5b19589245851587f29886ab/Toxicologia-Veterinaria.pdf
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Can Cats Be Poisoned by Onions?