Onion Toxicity In Dogs and Cats

Onions are highly toxic to dogs and cats.


Shiba inu, and other Japanese breeds, are predisposed to greater effects from onion toxicity.

Fortunately, most cats have better sense than to eat onions, but onions that have been cooked with a tasty sauce may be attractive to both species. Grocery store onions are not the only culprit. Wild onions growing as volunteers in your yard are just as poisonous. Even rotten onions thrown out in the compost pile retain their toxic capabilities. Dietary supplements, cooking products (such as seasonings and flavorings) as well as juice have the potential for causing poisoning.

The dangerous poison results in anemia in its victim. “Heinz body” formation occurs, “tagging” the red blood cell for destruction by the immune system or even outright breakdown of cells because of increased fragility. If a sufficient number of red blood cells (RBCs) is destroyed, the result is too few red cells to carry sufficient oxygen for normal body function. Several days may pass between the ingestion of onions and onset of clinical signs.

One-half of one percent (0.5%) of a pet’s body weight in ingested onions is sufficient to cause toxicity. That equates to just 2.5 ounces of onion in a 30-pound dog. Cats and Japanese dog breeds (Shiba Inu, Akita) tend to have an even greater sensitivity to onion poisoning because of an inherited, non-fatal defect in red blood cell formation.

A pet concurrently on certain medications is placed at even greater risk for illness. These include, but are not limited to acetaminophen and sulfur-based antibiotics. Acetaminophen (the active ingredient in Tylenol) should never be administered to pets under any circumstances.

Treatment is aimed at removing the offending material. Your veterinarian will induce vomiting. He may also administer one or more treatments with activated charcoal. If anemia has reached dangerous levels, he may also begin a blood transfusion with type-matched blood. No specific antidote is available.

The toxic ingredient is in the organosulphoxide family. Think carbon molecules combined with sulfur. The combination makes a strong oxidizer, which results in damage to hemoglobin molecules in red blood cells.

See you Monday, Dr. Randolph.

6 Comments to “Onion Toxicity In Dogs and Cats”

  1. RumpyDog! 28 January 2012 at 7:16 pm #

    I wonder if Malamutes are also predisposed.

    • Dr. James W. Randolph 28 January 2012 at 8:17 pm #

      Welcome back, RumpyDog! None of the literature I used for Onion Toxicity In Dogs And Cats mentioned any breed predispositions other than Japanese breeds. Which, of course, made me wonder about Chinese breeds, but, apparently, there is sufficient genetic diversity between them that there is no evidence that they have special considerations. Bottom line: No onions for your dog or your cat! See you at next week’s Blog Hop! Dr. Randolph.

  2. Bassetmomma 28 January 2012 at 9:59 am #

    Wow! I didn’t know that! Great informational post!

    • Dr. James W. Randolph 28 January 2012 at 8:17 pm #

      Glad you enjoyed the “onion” post, Bassetmomma! Soon I may write one about how much I personally dislike onions. (But, who would read that?) See you next week at the Blog Hop! Dr. Randolph.

  3. Doctor Vet 28 January 2012 at 1:26 am #

    Thank you for explaining onion toxicity Dr. Randolph! That is one I explain to clients quite a bit. It seems to be in so many recipes, and clients want to share just a little – just not safe!

    • Dr. James W. Randolph 28 January 2012 at 8:31 pm #

      True, funny story (with the potential for a tragic outcome, but which came out OK). My father used to have a poodle named Ajax (grandson of Zeus and a great warrior). Ajax loved grapes, and Daddy would give him some almost every night. I explained to him that even one grape could wipe out his kidneys and kill him. Daddy insisted that “one a day couldn’t possibly hurt him.” Finally he relented, and Ajax never got sick from them. We humans can be so hardheaded! See you at next week’s Blog Hop, Dr. Vet!

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