No. Onions contain compounds that destroy red blood cells in dogs, causing haemolytic anaemia. All forms are toxic — raw, cooked, powdered, and in gravy or takeaway food.

How much onion is toxic to dogs?

As little as 15–30 g per kg of body weight can cause harm. A few tablespoons of onion gravy or leftover curry may be enough for a small dog. Use our onion toxicity calculator for guidance.

What are symptoms of onion poisoning?

Vomiting, diarrhoea, weakness, pale gums, rapid breathing, and dark urine may appear within one to five days as anaemia develops.

What should I do if my dog ate onion?

Phone your vet or Animal PoisonLine on 01202 509000 with the amount and your dog's weight. Do not wait for symptoms — anaemia may take days to appear.

Dog Health

Can Dogs Eat Onion UK?

Published 19 July 2026Last updated 19 July 20262 min read

Quick answer

No — dogs must not eat onion. Onions destroy red blood cells, causing anaemia that may appear days later. All forms count — raw, cooked, powder, and in gravy or curry. If your dog ate onion, use our onion toxicity calculator and phone your vet or Animal PoisonLine on 01202 509000.

Key takeaways

No. Onions contain compounds that destroy red blood cells in dogs, causing haemolytic anaemia. All forms are toxic — raw, cooked, powdered, and in gravy or takeaway food.
As little as 15–30 g per kg of body weight can cause harm. A few tablespoons of onion gravy or leftover curry may be enough for a small dog. Use our onion toxicity calculator for guidance.
Vomiting, diarrhoea, weakness, pale gums, rapid breathing, and dark urine may appear within one to five days as anaemia develops.

Why onion is toxic

Plants in the Allium family — onion, garlic, leeks, chives, and shallots — contain thiosulphates that damage red blood cells, causing haemolytic anaemia.

Hidden sources in UK homes:

Onion gravy and stock cubes
Curry, pizza, and takeaway meals
Baby food with onion powder
Seasoning mixes

Symptoms

Signs may not appear immediately — anaemia can develop over one to five days:

Vomiting and diarrhoea
Weakness and lethargy
Pale gums
Rapid breathing
Dark or reddish urine

What to do if your dog ate onion

Estimate the amount and note the form (raw, cooked, powder)
Use the onion toxicity calculator
Phone your vet or Animal PoisonLine (01202 509000, charges apply) with your dog's weight
Do not wait for symptoms

See onion and garlic poisoning for full guidance.

Safe alternatives

Plain cooked vegetables without seasoning — carrots, green beans, or plain rice — are safer treats. See what vegetables can dogs eat.

Sources & further reading

Facts in this guide are rewritten in plain English from publicly available UK advice. We name the organisation where a specific point comes from their guidance. Links below go to the original pages — use them to read the source material directly.

PETHEALTH+ is independent. These organisations do not sponsor, approve, or partner with this website. Guidance checked against sources listed below (last updated 2026-07-19).

Frequently Asked Questions

Can dogs eat onion?: No. Onions contain compounds that destroy red blood cells in dogs, causing haemolytic anaemia. All forms are toxic — raw, cooked, powdered, and in gravy or takeaway food.
How much onion is toxic to dogs?: As little as 15–30 g per kg of body weight can cause harm. A few tablespoons of onion gravy or leftover curry may be enough for a small dog. Use our onion toxicity calculator for guidance.
What are symptoms of onion poisoning?: Vomiting, diarrhoea, weakness, pale gums, rapid breathing, and dark urine may appear within one to five days as anaemia develops.
What should I do if my dog ate onion?: Phone your vet or Animal PoisonLine on 01202 509000 with the amount and your dog's weight. Do not wait for symptoms — anaemia may take days to appear.