Onion Poisoning (Allium Toxicosis) in Cats

Published on
Last updated on
6 min read

Key takeaways

Onion toxicosis is poisoning caused by ingestion of any form of the plants belonging to the Allium genus: onion, garlic, leek, shallot, scallion, and chive.

  • Allium species contain toxins that cause injury to red blood cells when ingested by cats
  • When larger amounts of onion are consumed, more blood cell damage results, and the consequences are potentially life-threatening
  • Any cat who has ingested a potentially dangerous amount of Allium species needs emergency care
  • Symptoms include lethargy, difficulty breathing, and pale gums
  • Inducing vomiting immediately after ingestion has the best prognosis
  • Treatment is supportive and includes IV fluids and blood transfusions
  • Prognosis depends on how much onion was consumed, the success of decontamination efforts, and how quickly the resulting anemia is identified and treated
Are you concerned?

Connect with a vet to get more information about your pet’s health.

Book an online vet

A closer look: Onion Poisoning (Allium Toxicosis) in Cats

Onions, garlic, chives, and other related plants are all part of the Allium genus, which are toxic to cats. Plants from this genus cause red blood cell damage in cats. Red blood cells are responsible for carrying oxygen to the body and for removing wastes in the form of carbon dioxide and other metabolites. If the rate of red blood cell damage outpaces the rate of red blood cell production by the body, anemia and other complications develop as the blood is no longer able to function at full capacity. Eventually metabolites and other wastes build up in body tissues, which can lead to widespread organ dysfunction.

Risk factors

Cats who never ingest onions, et. al., will never get allium toxicosis. All plants belonging to the Allium genus are highly toxic to cats and are more potent in their dried and powdered forms.

Unlike other toxicoses, no amount of onion is harmless to cats. Any amount of onion will cause red blood cell damage. This damage becomes clinically significant when the percentage of red blood cells affected is significantly large enough that the cat’s body cannot compensate for the loss. Healthy cats can cope with a degree of reduction in red blood cell count without showing any symptoms. Cats with concurrent illnesses that suppress red cell production (like chronic kidney disease) or destroy red cells (like feline infectious anemia) are more vulnerable to the effects of onion ingestion.

Cooking does not lessen the toxicity of onions.

Determining the amount of onion that is potentially dangerous is complicated and best left to a veterinary professional.

Since the resulting anemia has the potential to be life-threatening, onion toxicosis is an emergency, both when a cat has just eaten a dangerous amount of onion and when it has developed anemia days after onion ingestion.

Possible causes

Onion toxicosis in cats is caused by consumption of any plant belonging to the Allium genus, including:

  • Onion
  • Garlic
  • Scallion
  • Shallot
  • Chive
  • Leek

Allium species contain an array of organosulfides which convert to sulfur-containing organic compounds following ingestion. These compounds cause oxidative injury to feline red blood cells. When larger amounts of onion are consumed, more blood cell damage results, and the consequences are potentially life-threatening.

Onion toxicosis can result from both a single large ingestion of onion, or after buildup that occurs over time when small amounts of onion are ingested regularly.

Main symptoms

Symptoms of toxicosis usually appear 2-5 days after ingestion, because it takes that long for enough red blood cell damage to occur.

Testing and diagnosis

The symptoms of anemia are vague and nonspecific, especially when the anemia is mild. Diagnosis is revealed during routine blood work performed on any sick cat. Even with no known history of onion ingestion, a cat with onion toxicosis shows characteristic changes on a complete blood count (CBC).

Most cats with the generalized signs of illness described above receive the following work-up:

  • Physical examination
  • Detailed blood work
  • Urinalysis

Steps to Recovery

There is no antidote for onion toxicosis. When the ingestion is known to have occurred (and prior to onset of clinical signs), treatment focuses on gastrointestinal decontamination. Prompt veterinary care for inducing vomiting provides the best opportunity to remove at least some of the onion from the cat’s system. There is no way to safely or effectively induce vomiting in cats at home.

Once symptoms start to appear, therapy is supportive and includes:

  • Fluid therapy
  • Blood transfusions
  • Supplemental oxygen The entire time red blood cells are being destroyed, the cat’s bone marrow is producing new red blood cells, the same as it always does. Once the sulfur-containing oxidants are no longer in the animal's system, the damage will stop and the red blood cell count catches up.

Prognosis depends primarily on the amount of toxin ingested. Of the Allium species, garlic is the most potent, and dried/powder forms are also more concentrated


Onion toxicosis is not contagious. Prevention depends on diligent storage of produce and trash as well as avoiding feeding any foods containing onion, garlic, chives, or leeks.

Is Onion Poisoning (Allium Toxicosis) in Cats common?

Onion toxicosis is uncommon. Even though cats are more sensitive to the toxins in onions than dogs, they are less commonly poisoned because they are typically discriminating eaters and usually do not consume enough onion for it to be dangerous.

Typical Treatment

Typical treatment of onion toxicosis may include:

  • Gastrointestinal decontamination
  • IV fluids
  • Blood transfusion
  • Supplemental oxygen


Tina Wismer, DVM, DABVT, DABT - Writing for Veterinary Partner
Renee Schmid, DVM, DABVT, DABT; Ahna Brutlag, DVM, MS, DABT, DABVT; Lynn Buzhardt, DVM - Writing for VCA Animal Hospitals
R.B. Cope, BSc, BVSc, PhD - Writing for dvm360®
Sharon M. Gwaltney-Brant, DVM, PhD, DABVT, DABT - Writing for Merck Veterinary Manual

Our editorial committee

Our medical review team is responsible for validating and maintaining the quality of our medical information.