Onion Poisoning (Allium Toxicosis) in Cats


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 multiple organosulfides 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. Inducing vomiting immediately after ingestion has the best prognosis. If enough red blood cells are damaged, signs of anemia develop within days.

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.

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. 

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 the consumption of any plant belonging to the allium genus:

• 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. Symptoms include:  

Lethargy • Weakness  • Exercise intolerance  • Decreased appetite • Rapid, shallow breathing (tachypnea)

Pale gums

Detailed Characterization

Clinical signs of onion toxicosis may be divided into early and late onset symptoms.

In the first few hours following the ingestion, some cats show showing symptoms of gastroenteritis:

Vomiting • Diarrhea • Loss of appetite 

Later, once the hematological changes start, symptoms of anemia described above develop

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: Fluid therapy is useful for maintaining blood pressure and hydration.  

• Blood transfusion: If enough red blood cells are damaged to cause life-threatening anemia, a blood transfusion is the best way to keep the cat alive until it makes enough new red cells to recover. 

• Supplemental oxygen: Red blood cells carry oxygen and when they are in short supply, low oxygen levels (hypoxia) result. Supplemental oxygen helps bridge that gap. 

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 Common in Cats?

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

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