Help! My Dog Ate Onion

Emergency care (details below)

What To Do If A Pet Eats Onion

  1. Toxin absorption can be prevented by immediately seeing a vet to induce vomiting
  2. If onion has been absorbed then daily blood tests are needed to monitor anaemia
  3. Please see a vet even if the amount seems tiny: pets vary in sensitivity and the toxic dose is low

now dive deeper…

Onion ingestion is the third most common poisoning vets see in Adelaide. Like so many pet poisons, onion is a trap we accidentally lay for our pets.

Cooking and leftovers are the problem. Raw onion advertises its toxicity so well that no self-respecting dog or cat would eat it. Add a bit of heat, some other ingredients, and suddenly it’s nice and tasty without the unpleasant warning flavours that keep our pets safe.

How Much Onion Is Dangerous?

For most dogs, as little as 2.5g of onion per kilogram of body weight can produce serious effects. That equals only 15g in a Jack Russell Terrier. Similar results have been observed with garlic, and it’s probably the same for related vegetables.*

Two essential facts:

  1. All dogs who eat onion should be made to vomit as susceptibility varies.
  2. Exposure is cumulative. The lower line on the graph at the top shows how slowly dogs recover. Any more onion in this period will add further damage and increase risk.

*The study (link below) used 5g/kg of dehydrated onion, which is probably equivalent to cooked onion. An equivalent amount of fresh onion would be heavier. Some of the dogs developed life-threatening anaemia so the hazardous dose is clearly lower; I have arbitrarily chosen half.

Is Garlic Toxic To Pets?

Yes. Experience tells us that the entire onion family is dangerous. That includes:

  • All onion varieties
  • Garlic
  • Leeks
  • Spring onions
  • Shallots
  • Even chives

Why Are Onions Poisonous?

Isn’t it strange that humans can happily eat onion but many other animals can’t. The reason is quite unexpected: it’s all about antioxidants.

Onion, whether cooked or raw, contains sulfur compounds that cause oxidative damage. The red blood cell in dogs and cats has a low antioxidant capacity. Put these together and disaster ensues.

That means that when dogs or cats eat onion, the red blood cells undergo chemical attack. Two serious consequences arise:

  1. Haemoglobin (the molecule that carries oxygen) is deactivated
  2. Cell walls are ruptured and red blood cells are destroyed

The result is anaemia and a reduced ability to deliver oxygen to the body.

Symptoms Of Onion Poisoning

Signs of onion poisoning typically appear after 1 to 3 days when the anaemia develops. They include:

  • Lethargy
  • Weakness
  • Laboured breathing
  • Pale gums
  • Collapse

You might also notice red urine and yellow eyes from pigments released by the destruction of red blood cells.

Treatment Of Onion Poisoning

Dogs that have eaten onion within the last hour can be treated simply by making them vomit. After this time it’s likely that some will have been absorbed.

If so, vomiting may still be worthwhile followed by a dose of activated charcoal. However, there is no antidote for the toxin that reaches the bloodstream.

These dogs need daily monitoring via blood tests. Some will need oxygen support or transfusions but the good news is that most will recover uneventfully.

Have something to add? Comments are welcome below and will appear within 24 hours of lodging.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These help topics are from a series regularly posted on Facebook and Twitter. Subscribe via email here to never miss a story! The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.

Further Reading

Common dog & cat poisons of Adelaide

Harvey, J. W., & Rackear, D. (1985). Experimental onion-induced hemolytic anemia in dogs. Veterinary Pathology, 22(4), 387-392. Full text


3 Replies to “Help! My Dog Ate Onion”

  1. My dog actually ate garlic sauce off a plate I’m worried because his so allergic to things and had a huge reaction before to eating something we weren’t sure what it was , he almost died I’m worried he might be highly allergic to this more then other dogs that accidentally would lick or eat this , what should I do ?

    1. Michelle you should get him to a vet within 2 hours, and ideally within 30 minutes to induce vomiting. It’s unlikely he’ll be allergic to the garlic, but it’s certainly a serious toxin. if you miss the chance to get it out, take him for a visit to your vet tomorrow.

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