§ Toxic plants · Amaryllidaceae · Checked Oct 2026
Is common onion toxic to cats and dogs?
Yes. Common onion (Allium cepa) is toxic to cats and dogs, according to the ASPCA Animal Poison Control Center. Plant Smart rates its effects Critical, level 4 of 4.
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§ 010 · Signs
What to watch for
Signs include vomiting, anemia (pale gums), weakness, fast heartbeat, panting, blood in the urine, weak pulse, wobbliness or poor coordination, collapse and trouble breathing. Signs can start within hours; some take a day or more to show.
§ 020 · If it happened
What to do if your pet ate it
Call your vet or a pet poison hotline straight away, even if your pet seems fine: the ASPCA Animal Poison Control Center, (888) 426-4435, or Pet Poison Helpline, (855) 764-7661. Both are open 24 hours and charge a fee. Have the plant or a photo of it to hand, and don’t make your pet vomit unless a vet tells you to.
§ 030 · Same family
Other Amaryllidaceae plants toxic to pets
Common onion belongs to the Amaryllidaceae family. ASPCA lists these relatives too.
§ 040 · Questions
Questions about common onion and pets
Is common onion toxic to cats?
Yes. ASPCA lists common onion as toxic to cats.
Is common onion toxic to dogs?
Yes. ASPCA lists common onion as toxic to dogs.
What happens if my pet eats common onion?
Signs include vomiting, anemia (pale gums), weakness, fast heartbeat, panting, blood in the urine, weak pulse, wobbliness or poor coordination, collapse and trouble breathing. Plant Smart rates it Critical, level 4 of 4.
What should I do if my pet ate it?
Call your vet or a pet poison hotline right away, even before signs appear: the ASPCA Animal Poison Control Center at (888) 426-4435, or Pet Poison Helpline at (855) 764-7661. Both charge a fee. Have the plant, or a photo of it, to hand.
What else is common onion called?
Common onion is also sold or known as shallot and tree onion.