Onions and Garlic: Why Alliums Are Toxic to Dogs

Nobody feeds their dog an onion. They feed it gravy, or a bit of leftover curry, and that is exactly how the onion gets in.

Nobody sits down and feeds their dog a raw onion. That is not how this happens.

It happens with the last of the gravy, a scraped plate after a curry, a bin bag raided while you were out, or a spoonful of leftover stew handed over by somebody who thought they were being kind. The onion family is in nearly every savoury thing we cook, which makes it one of the easiest poisons in the house to give a dog by accident.

What it does

Onions, garlic, chives, leeks and shallots all contain compounds that damage a dog's red blood cells. Do enough of that and the blood struggles to carry oxygen, which is anaemia.

The effect is dose-related, so a crumb of onion off a dropped burger is unlikely to trouble a big dog. A bowl of leftover casserole is a different conversation, and so is anything concentrated.

Concentrated is the word that matters

Cooking does not defuse alliums. If anything it is the drying and concentrating that causes the trouble.

Garlic powder, onion granules, stock cubes, gravy, dried soup mix: these pack the same compounds into a far smaller volume. A teaspoon of onion powder carries much more punch than a slice of raw onion, which is why gravy is such a common culprit and such an easy one to overlook. You do not think of gravy as onion.

While we are here: garlic is not a flea remedy. It gets recommended online as a natural supplement and it should not be fed to dogs deliberately in any form.

The damage shows up late

The stomach upset, if it comes, arrives early. The red blood cell damage takes a few days.

So the dog that wolfed the leftovers on Sunday and seemed absolutely fine on Monday is not necessarily in the clear. That is the reason to ring for advice while your dog still looks well, rather than waiting to be convinced.

What to do

1. Ring your vet or a poison line. Tell them what was eaten, in what form (raw, cooked, powdered), roughly how much, and how big your dog is. Those details genuinely change the answer.
2. Keep any packaging from soup mixes, stock or ready meals.

In the UK, the Animal PoisonLine. In the US, the ASPCA Animal Poison Control Center.

Do not try to make your dog sick unless you have been told to.

What to watch for over the following days

• Vomiting and diarrhoea early on
• Tiredness and weakness
• Pale gums
• Fast breathing and a racing heart
• Red or brown urine

Pale gums and discoloured urine are the two that mean go now. Both suggest red blood cells are being destroyed, and that needs a vet the same day.

Christmas, curry houses and kind strangers

Allium poisonings cluster around big meals, which is why Christmas and Thanksgiving are reliably busy. Roast dinners, stuffing, gravy, curry, and the bin bag afterwards holding all of it.

Two habits fix most of it. Keep bin bags behind a door rather than by it, and be unembarrassed about telling friends and family not to feed your dog from their plate, however small the piece.

The everyday version nobody thinks about

Baby food. A great many savoury baby foods and pouches contain onion powder, and they are exactly the sort of thing a dog is fed as a treat, or licks off a dropped spoon, in a house with a small child.

Worth reading the label on anything you routinely share.

Sources

This article was written using guidance from ASPCA Animal Poison Control Center, a leading 24/7 animal poison control resource in the United States. This guidance is for general information and does not replace a consultation with your own veterinarian. In an emergency, always contact a vet. Read [how we write our health guidance](https://rochsociety.com/how-we-write-our-health-guidance/). Last reviewed July 2026.