Onions and dogs: garlic, leeks, chives and the toxic amounts
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
If your dog has eaten onion, garlic, leek, shallot or chives, raw, cooked or powdered, call your vet or an animal poison helpline — in the US the ASPCA Animal Poison Control Center, (888) 426-4435 (a consultation fee may apply), in the UK Animal PoisonLine, 01202 509 000, in France the CNITV in Lyon, 04 78 87 10 40. Note what was eaten (fresh vegetable, cooked dish, powder, soup), roughly how much and when. Do not make your dog vomit yourself: that is the vet’s call. One key point: even if your dog is perfectly well today, the signs of this poisoning often appear several days later. A small bite of an oniony dish is rarely serious for a large dog, but only a calculation based on body weight can tell.
Contents · 7 sections
Why onions and garlic are toxic to dogs
Onion, garlic, leek, shallot and chives all belong to the genus Allium. They contain sulphur compounds released when they are chopped, cooked or chewed. Once absorbed, these compounds oxidise red blood cells: clumps called Heinz bodies form on them, their membrane weakens, and the cells are destroyed. This is haemolytic anaemia: the blood carries oxygen less well. Cooking does not remove the danger, and according to the Merck Veterinary Manual, garlic is 3 to 5 times more toxic than onion. Poisonings most often involve concentrated forms: dehydrated, powdered or flaked onion or garlic, and soup mixes.
How much is too much
The Merck Veterinary Manual states that in dogs, eating 15 to 30 g of raw onion per kilo of body weight has caused clinical signs. A study by Tang and colleagues, published in 2008 in the Journal of Veterinary Pharmacology and Therapeutics, fed dogs cooked onion at 30 g/kg a day for 2 days (see the study): Heinz bodies rose from day one and peaked on day three, and the drop in red blood cells became clear by day five.
The effect adds up when a dog eats it several days in a row. A study by Lee and colleagues, published in 2000 in the American Journal of Veterinary Research, gave dogs a garlic extract equal to 5 g of fresh garlic per kilo, once a day for 7 days (see the study). Red blood cell counts fell to a low point between days 9 and 11, with Heinz bodies and misshapen red cells, even though no dog developed full-blown anaemia. The authors conclude that foods containing garlic should not be fed to dogs. In other words, small repeated amounts (daily table scraps, “garlic against fleas”) are not harmless.
Table: reference amounts by body weight
Using the published threshold (15 to 30 g of raw onion per kilo, Merck Veterinary Manual) and the weight of a medium onion (110 g) and a garlic clove (3 g) from the USDA FoodData Central database, we calculated the single-meal amounts associated with clinical signs. For garlic, we applied the “3 to 5 times more toxic” ratio to the lower threshold.
| Dog’s weight | Raw onion (15-30 g/kg) | In medium onions | Fresh garlic, equivalent marker |
|---|---|---|---|
| 5 kg (11 lb) | 75 to 150 g | ⅔ to 1.4 onions | 15 to 25 g, i.e. 5 to 8 cloves |
| 10 kg (22 lb) | 150 to 300 g | 1.4 to 2.7 onions | 30 to 50 g, i.e. 10 to 17 cloves |
| 20 kg (44 lb) | 300 to 600 g | 2.7 to 5.5 onions | 60 to 100 g, i.e. 20 to 33 cloves |
| 30 kg (66 lb) | 450 to 900 g | 4 to 8 onions | 90 to 150 g, i.e. 30 to 50 cloves |
| 40 kg (88 lb) | 600 to 1,200 g | 5.5 to 11 onions | 120 to 200 g, i.e. 40 to 67 cloves |
These figures apply to a single meal of the fresh vegetable. They do not apply to powders and dehydrated products, which are far more concentrated, nor to repeated intake over several days, which lowers the threshold considerably. A small, elderly or already ill dog may react sooner. This table helps you gauge the risk before you call; it does not replace your vet’s advice.
Signs and when they appear
- In the first 24 hours: often nothing visible, even though Heinz bodies are already forming in the blood (Merck Veterinary Manual).
- Between 1 and 5 days later: tiredness, loss of appetite, fast breathing, fast heartbeat, pale or yellowish gums, weakness on exercise, dark (red or brown) urine.
- Severe cases: collapse. The vet may need to give oxygen or a blood transfusion; a blood test confirms the anaemia.
Timings from the Merck Veterinary Manual (signs usually “a few days” after exposure) and the Tang study. If your dog ate onion or garlic this week and becomes tired or pale, tell your vet: they will not necessarily make the connection on their own.
Onion hidden in everyday food
- Stock cubes, soups, gravies and sauces: onion and garlic powder are very common on the ingredient list.
- Ready meals and leftovers: pizza, quiche, lasagne, bolognese, stews, stuffing, flavoured crisps, barbecue marinades.
- Dumplings and dim sum: a case published by Yamato and colleagues in 2005 in the Journal of the American Animal Hospital Association (see the study) describes severe anaemia in a miniature schnauzer after eating Chinese dumplings containing chives and garlic.
- Baby food: some jars contain onion; read the label before offering it to a sick dog that is off its food.
- “Natural” products: garlic is sometimes sold as a parasite remedy; the studies above show it damages dogs’ red blood cells.
Prevention at home
- No seasoned table scraps: a home-cooked diet for dogs is made without onion or garlic, see our comparison of kibble or home-cooked diet.
- Store onions, shallots and garlic bulbs in a cupboard or a closed basket, not on the floor.
- At festive meals, watch the plates and the bin, along with the chocolate: see the toxic dose of chocolate by weight. More pointers on the dog food page.
Frequently asked questions
My dog ate a small piece of onion, is it serious?
For a medium-sized dog, a small piece usually stays well below the published threshold, but that is not true for a 3 kg dog or for onion powder. Call your vet or a poison helpline: they will work out the risk from your dog’s weight.
Is cooked onion less dangerous than raw onion?
No: cooking does not destroy the compounds responsible. In the Tang study, it was cooked onion that caused anaemia.
How long after eating onion does a dog get sick?
Signs of anaemia usually appear after a few days (often between 1 and 5 days), sometimes later with repeated intake. That is why you should call as soon as you know your dog ate some.
Is a little garlic good for dogs?
No. Garlic is more toxic than onion, and even small amounts given several days in a row oxidise a dog’s red blood cells. For parasites, ask your vet for a suitable treatment.
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This guide is part of Planète Pets’s Dogs universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
