Updated 2026-08-07 · Source: ASPCA Animal Poison Control — People Foods to Avoid Feeding Your Pets; ASPCA Animal Poison Control — Toxic and Non-Toxic Plants database · Free · No sign-up
No — onions are toxic to cats, even in small amounts. Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 now.
If your cat may have eaten something harmful — or any part of a lily — call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 right now — don't wait for symptoms. A consultation fee may apply to the ASPCA hotline.
Verdict for cats
Toxic
Severity
5 / 5 — Emergency — can be fatal, and small amounts can matter. Call now.
Safe amount
None
Category
Vegetable
Source
ASPCA Animal Poison Control — People Foods to Avoid Feeding Your Pets; ASPCA Animal Poison Control — Toxic and Non-Toxic Plants database · reviewed 2026-08-07 · confidence: high
Why
Cats are more susceptible to Allium poisoning than dogs, so a smaller amount matters more. Signs of anemia can take a few days to appear, which is why vets want to hear about the exposure straight away rather than after symptoms.
Signs to watch for if your cat has eaten onions
Vomiting, drooling or diarrhea
Weakness, tiredness or collapse
Pale or yellow gums
Red or brown urine
Fast breathing and a fast heart rate — signs can take 1–5 days to appear
Signs vary with the amount and with the individual pet, and some appear only after a day or more. Their absence does not mean your cat is in the clear — call rather than watch.
What to do now
Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 straight away. Tell them what your cat ate, roughly how much, and when, and take the packaging with you. Don't wait for symptoms — with several poisons the harm is done before a pet looks ill.
Never induce vomiting and never give any medicine unless a vet tells you to. With some substances it causes more damage than the poison. This page tells you when to get help — it never tells you how to treat at home.
Safer alternatives for cats
A small piece of plain cooked chicken or turkey
Plain cooked fish, boneless and unseasoned
A vet-approved commercial cat treat, kept to under a tenth of daily calories
Cat grass grown indoors instead of houseplants
Fresh water — a fountain tempts many cats to drink more
Verdicts are transcribed from the cited veterinary sources, never inferred. Where a source establishes a finding for one species only, the other species is left null and the page says to ask your vet — a dog finding is never copied onto a cat.
This page is a reference, not veterinary advice or a diagnosis. CanMyPetEat is a reference, not veterinary advice or a diagnosis. It tells you when to get help — never how to treat at home. Never induce vomiting or give any medicine unless a vet tells you to. Individual pets vary and toxicity guidance changes; your vet and the ASPCA Animal Poison Control Center are the authority.
No — onions are toxic to cats, even in small amounts. Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 now. Cats are more susceptible to Allium poisoning than dogs, so a smaller amount matters more. Signs of anemia can take a few days to appear, which is why vets want to hear about the exposure straight away rather than after symptoms.
What happens if a cat eats onions?
Watch for: Vomiting, drooling or diarrhea; Weakness, tiredness or collapse; Pale or yellow gums; Red or brown urine; Fast breathing and a fast heart rate — signs can take 1–5 days to appear. Signs can take hours or, for some poisons, a day or more to appear, so call your vet rather than waiting to see.
How many onions are dangerous for a cat?
There is no known safe amount — small quantities have caused serious harm, so treat any exposure as urgent and call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435.