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. All forms count: raw, cooked, powdered, and dehydrated. Use the onion calculator, then phone your vet.

Is garlic less toxic than onion?

Garlic is still toxic — it contains the same compounds (thiosulphates and organosulphoxides) that damage red blood cells. Do not assume garlic supplements or leftover garlic bread are safe.

What are symptoms of onion poisoning in pets?

Vomiting, diarrhoea, weakness, pale gums, rapid breathing, and dark urine appear within one to five days as red blood cells are destroyed (haemolytic anaemia).

Can cats eat food with onion powder?

No. Cats are more sensitive than dogs to allium toxicity. Baby food, stock cubes, and takeaway meals often contain onion or garlic powder — check labels before sharing human food.

Should I wait to see if they get ill?

No. Red-cell damage can take days. Early decontamination is the point of phoning now. A pet that 'seems fine tonight' is not cleared.

Pet Care

Onion & Garlic Poisoning in Pets UK

Published 25 June 2026Last updated 13 August 20265 min read

Quick answer

Onions, garlic, leeks, chives, and shallots are toxic to dogs and cats. They destroy red blood cells, causing anaemia that may appear days later. If your pet ate onion-rich food — including gravy, curry, pizza, or garlic bread — use the onion & garlic calculator, then phone your vet or Animal PoisonLine on 01202 509000 with the amount and your pet's weight.

Key takeaways

Onions, garlic, leeks, chives and shallots destroy red blood cells in dogs and cats — all forms count, including powder and gravy.
As little as about 15–30 g/kg of onion can harm dogs; cats are generally more sensitive — leftover curry or gravy can be enough for a small pet.
Call your vet or Animal PoisonLine (01202 509000) with the amount and weight — do not wait for symptoms. Anaemia may take days. Use the calculator as a prompt.

Why alliums poison pets

Plants in the Allium family — onion, garlic, leeks, chives, shallots, and spring onions — contain compounds that damage red blood cells in dogs and cats, causing haemolytic anaemia.

Unlike chocolate, effects are not always immediate. Damage accumulates over one to five days as cells break down. That delay is why “they seem fine” is a dangerous stopping rule.

All forms are toxic:

Raw, fried, or roasted onion and garlic
Onion and garlic powder in stock cubes, gravies, and processed foods
Dehydrated onions in crisps, soup mixes, and ready meals
Leftover takeaway — curries, stir-fries, and Chinese dishes often contain concentrated alliums

Cats are generally more sensitive than dogs, but both species can become seriously ill.

Approximate risk by amount

Rough guide	Risk
Around 15–30 g onion per kg body weight	Haemolytic anaemia risk in dogs commonly cited
Garlic (any form)	Still toxic — often more concentrated than onion by weight
Onion/garlic powder, gravy, curry	Easy to underestimate — treat as potentially toxic
Cats	Generally more sensitive — never share allium-containing food

These are approximate bands only. Use the onion & garlic calculator to turn leftover weight into a prompt, then phone. Individual sensitivity varies; the tool is not a diagnosis.

Common UK exposure routes

Sunday roast gravy and stuffing
Garlic bread and pizza toppings
Baby food containing onion powder (never feed to cats)
Stock cubes dissolved in pet food by mistake
Leftover Chinese or Indian takeaway
Homemade treats with garlic (popular online recipes are unsafe)
Shopping bags left in the hallway — whole onions are a chew toy for some dogs

Owners often underestimate powdered forms — a teaspoon of onion powder can be more concentrated than a slice of fresh onion. “Just the gravy” is still allium.

Symptoms of allium toxicosis

Signs may develop 1–5 days after ingestion:

Vomiting and diarrhoea (early)
Weakness and lethargy
Pale or yellow-tinged gums
Rapid breathing or panting at rest
Dark or reddish-brown urine (haemoglobinuria)
Collapse in severe cases

Chronic small exposures — such as garlic supplements marketed for fleas — can cause gradual anaemia. Avoid any garlic products for pets. Flea control belongs with licensed preventatives, not kitchen herbs.

What to do if your pet ate onion or garlic

Estimate the amount — type of food, approximate weight, time eaten
Run the onion calculator if you have numbers
Phone your vet or Animal PoisonLine (01202 509000) — do not wait for symptoms
Do not induce vomiting unless your vet instructs you
Bring food packaging or takeaway containers if available
If advised to go in out of hours, use the out-of-hours directory

Veterinary treatment may include:

Induced vomiting and activated charcoal if ingestion was recent
Blood tests monitoring red cell count and haemoglobin
IV fluids and oxygen support if anaemic
Blood transfusion in severe cases

Hospitalisation allows monitoring as anaemia may worsen over several days. Chocolate and grapes are different poisons with different clocks — chocolate and grapes — but the first move is still the phone.

Delayed bloods and gravy maths

Vets often repeat a red-cell count over several days. A normal result tonight does not close the case if a lot of onion went in this afternoon. Pale gums and dark urine later in the week are why you were told not to wait.

Gravy is easy to get wrong: a few tablespoons on a small terrier or a cat can sit in the cited g/kg band. Powdered onion in a stock cube is concentrated. Baby food labelled “with onion” is a classic cat exposure when owners think they are being kind.

If both a dog and a cat stole from the same plate, run the calculator twice and phone for both. Cats generally need a lower threshold of concern.

Prevention

Never share human meals containing onion, garlic, or leeks
Read labels on stock cubes, gravies, and baby food
Warn guests and children not to feed table scraps
Avoid garlic flea treatments and herbal supplements containing alliums
Store onions and garlic out of reach

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 2026-08-13).

Frequently Asked Questions

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. All forms count: raw, cooked, powdered, and dehydrated. Use the onion calculator, then phone your vet.
Is garlic less toxic than onion?: Garlic is still toxic — it contains the same compounds (thiosulphates and organosulphoxides) that damage red blood cells. Do not assume garlic supplements or leftover garlic bread are safe.
What are symptoms of onion poisoning in pets?: Vomiting, diarrhoea, weakness, pale gums, rapid breathing, and dark urine appear within one to five days as red blood cells are destroyed (haemolytic anaemia).
Can cats eat food with onion powder?: No. Cats are more sensitive than dogs to allium toxicity. Baby food, stock cubes, and takeaway meals often contain onion or garlic powder — check labels before sharing human food.
Should I wait to see if they get ill?: No. Red-cell damage can take days. Early decontamination is the point of phoning now. A pet that 'seems fine tonight' is not cleared.