Can Cats Eat Onions?

We’re all tempted to give our cats a special treat. But while some veggies are safe for cats, other human foods can cause serious problems. Which leads us to wonder: Can cats safely eat onions? 

The answer, in short, is no. Under no circumstances should a cat eat onions. Onions, along with garlic, chives, and leeks, are all in the Allium family and are poisonous to cats. And while onion poisoning occurs in dogs as well, cats are much more susceptible. 

Can Cats Eat Onions?

No, cats should not eat onions. While a cat might bite into a raw onion, it’s more likely they will eat a food that has onions in it.  

Cooked onions are as toxic to cats as the raw onions, so keep kitty away from sauces, soups, gravy, pizza, and any other onion-containing food. Foods cooked with onion powder or dehydrated/freeze-dried onions are equally—or even more likely—to cause poisoning if ingested. 

Why Are Onions Bad for Cats?

Onion toxicity causes significant stomach upset and damage to your cat’s red blood cells. This damage puts the red blood cells at risk for rupturing, causing life-threatening anemia.  

Red blood cells carry oxygen, and when these cells rupture, your cat has less oxygen in the body to survive. This destruction of red blood cells can also affect your cat’s lungs, liver, and kidneys. 

How Much Onion Is Toxic to Cats?

Onion poisoning in cats is caused by a toxic compound in the Allium plant called N-propyl disulfide.  

Although any amount of onion ingestion can cause stomach upset, the most severe signs occur when more than 5 grams of onions per kilogram of their body weight, or 0.5% of their body weight in kilograms, is ingested. This is the toxic dose—however, onion toxicity has been reported in cats after ingestion of less than 1 teaspoon of cooked onions. 

Something very important to consider is that onion powder is much more potent than an onion itself. Therefore, a small amount of onion powder can be toxic to cats. 

For reference, one medium onion weighs about ½ pound (226 grams), which is equal to just 1 tablespoon of onion powder. 

Symptoms of Onion Poisoning in Cats

Onion poisoning may not be evident immediately. Symptoms can be delayed until a significant amount of red blood cells have been damaged. The onset time for developing anemia can be as soon as 12 hours after ingestion, but it’s typically delayed until two to five days after exposure. 

The most common reported signs of onion poisoning in cats are vomiting, diarrhea, and lethargy, but other symptoms can include: 

• Initial non-specific signs: 

  • Nausea 

  • Drooling 

  • Oral irritation 

  • Abdominal pain 

• Signs of anemia and secondary damage to liver and/or kidneys: 

  • Pale, yellow, blue, gray, or brown gums and other mucous membranes in the body

  • Lethargy, depression 

  • Increased heart rate 

  • Increased respiratory rate (short, shallow breaths) 

  • Weakness 

  • Exercise intolerance 

  • Dark urine 

  • Yellowing of the skin and whites of the eyes 

  • Collapse 

  • Seizures 

  • Death 

My Cat Ate an Onion—Now What?

If your cat ate an onion or a food containing onions, or even if you only suspect they did so, they should be seen by their veterinarian or an emergency veterinarian as soon as possible. The earlier medical intervention takes place, the better outcome for your cat. 

It’s also recommended that you or your veterinarian call the Pet Poison Helpline at 855-764-7661 to speak to a veterinary toxicologist about how best to treat your cat’s exposure to onions.  

Onion poisoning in cats can be treated with prompt medical attention and intervention before too much red blood cell destruction occurs. 

Treatment of Onion Toxicity in Cats

If your cat eats onions, they may need to stay in the hospital for treatment and monitoring. 

If the onion was eaten recently (within the last two hours), your vet might try to make your cat vomit and give them activated charcoal to help absorb the toxin. 

Never try to make your cat vomit at home unless your vet tells you to. It could cause more harm. 

The vet will check your cat’s red blood cell levels and may run blood and urine tests to see if their organs—like the liver or kidneys—have been affected. Some cats might need a blood transfusion or extra oxygen if they’ve lost too many red blood cells. 

Your cat will likely get IV fluids and medicine to help with any stomach or liver problems. If they recover, your vet may want to recheck their blood in the coming weeks to make sure they're healing well. 

Most cats get better with fast treatment, but serious cases can be harder to treat—especially if the poisoning caused anemia or organ damage.