What to do if your pet ate it
Contact your vet or a poison line right away, report how much Onion was eaten and your pet's weight, and keep any packaging or leftovers. Do not induce vomiting unless your vet tells you to.
Signs to watch for
- Vomiting and diarrhoea
- Lethargy and weakness
- Loss of appetite
- Severe: tremors, breathing trouble, collapse
If your pet shows vomiting, lethargy or any unusual behaviour after eating Onion, go to the nearest emergency vet immediately.
Dogs and cats carry the same rating (Do not feed), so the notes below hold for either pet.
Other foods that are toxic or dangerous
The full A–Z food list groups every food by verdict for each species.
Why these cautions matter
Garlic and onion damage a pet's red blood cells and can bring on anaemia. Signs are often delayed for several days, so looking fine straight afterwards does not rule it out.
Frequently asked questions
Can cats eat Onion?
NO — do not feed. Toxic. Damages red blood cells (hemolytic anemia). Powdered onion is concentrated. Danger can appear 1–5 days later.
What if my cat already ate Onion?
Call your vet or a poison line now with the amount of Onion eaten and your cat's weight, and do not induce vomiting unless a vet tells you to. If Onion was eaten and you then see vomiting, lethargy, tremors or breathing changes, go straight to the nearest emergency clinic.
Is there a safe amount of Onion for cats?
There is no accepted safe dose of Onion for cats; it is classed as toxic or dangerous, and reactions vary with the individual animal, so it is not something to feed at any amount.
How often can cats have Onion?
Onion is not something to feed at any interval; it stays off the menu entirely.
What are safer treats than Onion for cats?
Pick from the safe list instead — Arugula or Bok choy carry none of the risk that Onion does, and they work better as an everyday treat.