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.

Typical signs of anemia are pale gums and skin, rapid breathing and possibly rapid heart rate.

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.


  1. I have a 7-1/2 year old shiba inu mix that ate wild onions. He has been sick off and on for one month now. We took him to the vet and they did blood tests. Before they had the results they prescribed an antibiotic and prednisone that cost over $200 for both. He threw up every pill we gave him. They did a seond blood test and said that whatever was causing his problems must be repairing itself. That was 10 days ago. Now he is breathing heavy and won’t eat anything. He is drinking water though. He can hardly get up to drink and collapses by the water bowl. The vet just closed for the day so I will have to wait until they open to bring him in again. What is your opinion of what is wrong with my dog?

    • I am so sorry that your pet is having difficulty. I wish I could help but there are literally thousands of things that could be causing the collection of signs you’re seeing. Perhaps you should consider a second opinion?

  2. Can’t figure out why one of our cats seems obsessed with the wild onions in our yard. He is almost 11 and we have a cat fence around our large privacy fenced yard so that all the cats can have the yard to themselves. The only problem is one of them loves to chew on the wild onions. He would always come in with onion breathe. One day I saw an article that explained how toxic they were and I have since tried to kill the onions or keep him from eating them, but he always seems to find one. Aside from keeping him from going outsold all together I am not sure what to do.

    He was recently diagonosed with lymphoma as well and they had to remove three large masses from his intestine and about 8 inches of intestine. He just started chemo last week and has started to finally eat again and wanders around outside with our close supervision. The first thing he does it go right to the onions. It’s very frustrating.

    I can’t help but feel they have somehow contributed to his condition , even though He is quite old. But I just don’t know what to do. If he manages to recover fully I really need to figure out how to Eliminate the onions, because he refuses to leave them alone.

    • I feel it is more likely that the interest in onions is a result, not a cause. “Pica” is a condition in which patients (of all species) eat items that are abnormal, usually because a medical condition is driving the taste or craving. I pray that your kitty responds well to treatment and that you can enjoy the additional time you have together.

    • 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.

  3. 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!

    • 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!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.