🧅 My Dog Ate Onion or Garlic. How Much Is Dangerous?
Onions, garlic, leeks, chives and shallots damage a dog's red blood cells, and the damage shows up 3 to 5 days later as anaemia, not as vomiting tonight. Dose decides everything: a slice of onion off a burger is rarely a problem for a Labrador; a whole onion in a stew, a garlic-heavy dish, or a spoon of onion powder can be. Work out grams per kilo below.
Onions and garlic dose checker
Your dog's weight plus what went in gives the dose per kilo and the urgency. Estimating? Assume the worst case.
How much onion or garlic is toxic to a dog?
| Level | Onion-equivalent | What it means |
|---|---|---|
| Action level | about 5 g/kg (0.5% of body weight) | The point at which vets recommend decontamination and blood checks. For a 10 kg dog: 50 g, half a medium onion. |
| Documented anaemia | 15 to 30 g/kg | Merck's range for clinical signs in dogs. For a 10 kg dog: 150 to 300 g, one to two onions. |
| Garlic | 3 to 5 times as potent | 1 g of garlic counts as about 5 g of onion; a clove is 3 g. Garlic supplements and garlic-heavy dishes matter. |
| Powders | far more concentrated | Dried onion is roughly nine times as concentrated as fresh; garlic powder more again. A tablespoon of onion powder is a whole onion. |
| Cats | 5 g/kg, or a teaspoon of cooked onion | Cats are much more sensitive. Baby food with onion powder has poisoned cats. |
Cooking, frying, dehydrating and powdering do not remove the toxin (n-propyl disulphide and related sulphoxides), which oxidises haemoglobin and makes red cells burst. Leeks, chives, shallots, spring onions and wild garlic are all in the same family.
Symptoms and timeline
| Time after eating | What you may see |
|---|---|
| 0 to 24 hours | Often nothing; sometimes vomiting, diarrhoea, drooling or a sore belly from the irritation. Heinz bodies begin forming inside red cells within 24 hours. |
| Days 1 to 3 | Methaemoglobin peaks around 72 hours: gums may look brownish or pale, breathing faster. |
| Days 3 to 5 | Haemolysis: pale or yellow gums, weakness, exercise intolerance, fast heart and breathing, dark red or brown urine, collapse in severe cases. |
What the vet will do
Induce vomiting if the meal was within about 2 hours, sometimes activated charcoal, then a baseline blood count and a repeat around days 3 to 5 to catch a falling packed cell volume. Mild cases are watched at home. Anaemic dogs get IV fluids to protect the kidneys from haemoglobin, oxygen if needed, and a transfusion if the anaemia is severe. Recovery takes 1 to 2 weeks as new red cells are made.
What to do right now
- Weigh what is left and estimate what went in: a medium onion is about 110 g, a clove of garlic 3 g.
- Call your vet or a poison line with the grams and your dog's weight: Pet Poison Helpline (US/CA) 855-764-7661 · ASPCA Animal Poison Control 888-426-4435 · Animal PoisonLine (UK) 01202 509000 · Ireland and elsewhere: your vet or the nearest emergency clinic. Poison lines charge a fee; they are worth it.
- Do not induce vomiting at home without instructions.
- Check gums daily for 5 days: press the gum, it should go from white back to pink in under 2 seconds. Pale, yellow or brownish gums, or dark urine, mean go now.
Onions and garlic FAQ
How much onion is toxic to dogs?
About 5 g of onion per kg of dog (0.5 percent of body weight) is the level vets act on; 15 to 30 g/kg has caused clinical anaemia. Half a medium onion is enough for a 10 kg dog to need a vet call.
Is garlic more toxic than onion for dogs?
Yes, per gram: 3 to 5 times as potent, and garlic powder is more concentrated again. The occasional garlic-flavoured treat is not the problem; garlic supplements, garlic bread binges and powders are.
My dog ate a small piece of onion. What should I do?
For most dogs, a slice or ring is far below the action level. Skip onion for a week, watch the gums and energy for 5 days, and call if your dog is tiny, a Japanese breed, or already unwell.
How long after eating onion will a dog get sick?
Stomach upset can start within hours, but the anaemia shows 3 to 5 days later. A dog that seems fine the next morning is not out of the woods; check gums through day 5.
Does cooking onion make it safe for dogs?
No. Cooked, fried, dried and powdered onion and garlic keep the toxin. Onion soup, gravy, stuffing and takeaway curries are common sources.
Related
Sources: Merck Veterinary Manual, Garlic and Onion (Allium spp) Toxicosis in Animals (15 to 30 g/kg dogs; garlic 3 to 5 times as toxic; timeline); Cope, Allium species poisoning in dogs and cats, Veterinary Medicine 2005 (0.5% body weight action level); Pet Poison Helpline Allium guidance. Thresholds are population figures for otherwise healthy adult animals; puppies, kittens, seniors and animals with kidney, liver or heart disease can be affected at lower doses. Last reviewed August 2026.