---
title: "Can Dogs Eat Onion UK?"
description: "UK guide — onions are toxic to dogs in all forms. Damage to red blood cells causes anaemia. Use our onion toxicity calculator and call Animal PoisonLine."
url: "https://pethealth.org.uk/health/can-dogs-eat-onion-uk"
canonical: "https://pethealth.org.uk/health/can-dogs-eat-onion-uk"
date_published: "2026-07-19"
date_modified: "2026-07-19"
source: "PETHEALTH+"
---

# Can Dogs Eat Onion UK?

**No — dogs must not eat onion.** Onions destroy red blood cells, causing **[anaemia](/glossary/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](/onion-toxicity-calculator)** and phone your vet or **Animal PoisonLine on 01202 509000**.

## 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

1. Estimate the amount and note the form (raw, cooked, powder)
2. Use the [onion toxicity calculator](/onion-toxicity-calculator)
3. Phone your vet or **Animal PoisonLine (01202 509000, charges apply)** with your dog's weight
4. Do not wait for symptoms

See [onion and garlic poisoning](/health/onion-garlic-poisoning-pets-uk) 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](/health/what-vegetables-can-dogs-eat-uk).

## FAQs

### 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.

## Sources

- [PDSA — Foods dogs should avoid](https://www.pdsa.org.uk/pet-help-and-advice/pet-health-hub)
- [Animal PoisonLine](https://www.animalpoisonline.co.uk)
- [RSPCA — Foods poisonous to dogs](https://www.rspca.org.uk/adviceandwelfare/pets)
- [BVA — Pet poisons](https://www.bva.co.uk)

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Last modified: 2026-07-19