How much onion is toxic to a dog?

Veterinary references cite roughly 15–30 grams per kg of body weight (over about 0.5% of body weight) as enough to cause significant red blood cell damage — for a 10 kg dog that's a medium onion. Onion powder is far more concentrated, and smaller repeated doses accumulate.

Is cooked onion also toxic to dogs?

Yes. Cooking does not destroy the toxic compounds. Raw, cooked, dried and powdered onion are all dangerous, which makes seasoned leftovers, gravies and takeout common culprits.

Are other onion-family vegetables dangerous too?

Yes — garlic, leeks, chives and shallots (all Allium species) damage red blood cells the same way. Garlic is more concentrated gram for gram.

How soon do symptoms of onion poisoning appear?

GI upset can show up within a day, but the anemia usually develops over one to several days after ingestion. Watch for lethargy, pale gums and dark urine, and call your vet if they appear.

Can Dogs Eat Onions? Vet-Sourced Answer

Can Dogs Eat Onions?

Toxic to dogs

No. Onions damage dogs' red blood cells and can cause hemolytic anemia. All forms are toxic — raw, cooked, powdered and in leftovers.

Quick facts

Quick facts
Verdict	Toxic
Risky amount	Eating more than about 0.5% of body weight in onions (roughly 15–30 g per kg) has caused clinically significant anemia in dogs; repeated smaller amounts also add up.
Key symptoms	Lethargy and weakness, Pale gums, Reddish or brown urine, Rapid breathing, Vomiting and diarrhea, Loss of appetite
What to do	Call your vet if your dog ate onions in any meaningful amount. Signs can be delayed by one to several days, so don't be reassured by a normal-looking dog on day one.

Why onions are toxic to dogs

Onions — like garlic, leeks and chives — contain organosulfur compounds (notably N-propyl disulfide) that oxidize hemoglobin in a dog’s red blood cells. The damaged cells (with so-called Heinz bodies) are destroyed by the body, and if enough are lost the dog becomes anemic. Dogs’ red blood cells are much more vulnerable to this than ours.

Every form counts: raw, cooked, fried, dehydrated and powdered. Onion powder in sauces, soups, broths and seasoned meat is one of the most common ways dogs get poisoned without anyone noticing.

How much is dangerous?

Veterinary references report significant red-blood-cell damage after dogs ate more than about 0.5% of their body weight in onions — roughly 15–30 g per kg. For a 10 kg dog that is a single medium onion. Two things make smaller amounts risky too: onion powder is far more concentrated than fresh onion, and the damage from small repeated doses accumulates over days.

Symptoms of onion poisoning

Vomiting or diarrhea may appear first, but the hallmark signs come from anemia and are often delayed by one to several days: lethargy, weakness, pale gums, fast breathing and reddish-brown urine.

What to do if your dog ate onions

Call your vet with an estimate of how much onion (or onion powder) your dog ate and when. Recent ingestions can be decontaminated; otherwise your vet may monitor red blood cell counts over the following days. Severe cases can need oxygen support or a blood transfusion, so early contact matters.

If your dog ate it

Call your vet if your dog ate onions in any meaningful amount. Signs can be delayed by one to several days, so don't be reassured by a normal-looking dog on day one.

In the US you can also call the ASPCA Animal Poison Control Center at (888) 426-4435 (a consultation fee may apply).

Frequently asked questions

How much onion is toxic to a dog?: Veterinary references cite roughly 15–30 grams per kg of body weight (over about 0.5% of body weight) as enough to cause significant red blood cell damage — for a 10 kg dog that's a medium onion. Onion powder is far more concentrated, and smaller repeated doses accumulate.
Is cooked onion also toxic to dogs?: Yes. Cooking does not destroy the toxic compounds. Raw, cooked, dried and powdered onion are all dangerous, which makes seasoned leftovers, gravies and takeout common culprits.
Are other onion-family vegetables dangerous too?: Yes — garlic, leeks, chives and shallots (all Allium species) damage red blood cells the same way. Garlic is more concentrated gram for gram.
How soon do symptoms of onion poisoning appear?: GI upset can show up within a day, but the anemia usually develops over one to several days after ingestion. Watch for lethargy, pale gums and dark urine, and call your vet if they appear.