Help! My Dog Ate Onion

Updated November 29, 2020

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.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These help topics are from a series regularly posted on email 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


29 Replies to “Help! My Dog Ate Onion”

  1. Our 9month off cocker- jack ate a tiny piece of spring onion on Monday and has been lethargic yesterday and today – no sickness of other symptoms that we can see – do you think she needs to go to the vets?

  2. hi, I have been feeding my dog (retriever of 40lb) cooked chicken, rice and carrots/broccoli with little amount of garlic and onion for a whole month now. I don’t see any symptoms or anything unusual yet and his pee and poop seems to be fine. I stopped adding the garlic and onions after I know about it. Should I get him checked at the vet. He does get tired easily though.

  3. Hi. I think my dog may have eaten some onion a few nights ago. She has gone off her food and is very lethargic. I rang my vet and they said to just monitor at home, but she doesn’t seem to have improved. It’s 10pm now so I can’t take her to the vet but have the option of an after hours call. I can take her first thing tomorrow but I don’t want to leave it any longer if it is putting her at risk. If we think she has eaten onion should we see someone asap?

    1. Hi Alex. Onion poisoning is much rarer than many other causes of lethargy and going off the food. I’m sorry I can’t give you any more information about what might be the problem or how urgent it is.

  4. Hi- My dog got into a little onion powder yesterday but threw up right after. He is a 70 lb lab 1 year old lab. He has been active, happy, and has had two solid stools since. He threw up a little bit again during the night but it had no onion smell to it. Has been fine since. Should I just monitor him now?

    1. Hi Chase. It all comes down to how much onion powder he ate. Certainly, if he vomited it back up again there is no risk but powder can be absorbed very quickly so I would go by how much he ate, not the fact that he vomited. When in doubt, always go to the vet and get a blood test to check for toxicity.

      1. Thank you for your help! It’s been 42 hours and no other signs (gums are red, stools are solid, active and good appetite)- however he threw up a little bile again last night. It’s hard to say how much he got but I would guess around 1-2 tbsp. Will he be okay with monitoring symptoms since he has been otherwise completely normal?

    2. Hi, my dog ate a little dice onion like half hour ago, after he ate his food. I’m worry about him. He is a German Spitz of about 22 pounds.

  5. My dog ate some of my chop suey that the tomato sauce had onion in it.. Should I induce vomiting? It’s been about 20 minutes and he seems perfectly fine

    1. Hi Mikaila. Regardless of the quantity, if you know a dog has been exposed to onion it’s always safest to get a vet to induce vomiting.

  6. Hey, so about 2 days ago my dog got to a left over pizza slice. She didn’t get it for long at all and do question if she even managed to eat any of it. I knew what she was planning so I cased her down. Just noticed on the box it has onion on it as I just drawn a blank at the time. She seems perfectly fine, no symptoms at all. Gums nice and pink. I’m just being on the safe side as I’ve seen people say for small consumption to keep and eye out and they should be fine and with her showing no symptoms. Is it safe to just keep an eye out on her? And obviously if shown any take her straight away. But if she keeps trooping on? Are we good? She’s has in the past eaten things she shouldn’t have and haven’t batted an eye. (Nothing recent)

      1. hi,

        i have a shihtzu and i was chopping onions, garlic and carrots last night.

        i fed a little bit of carrots to my dog and today she’s been acting strange. she hasn’t been her active self and i keep hearing her tummy.

        i’m freaking out!

      2. Unless you gave her onion the cause may be something else. It’s best you get a check up with your vet.

  7. My dog ate fish boiled with onion the following day she is very weak and had pale gums dont like to eat called home service vet she said its ok and its due to her old age since she is 16yrs old and that she only had an indigestion and onion is not the cause .
    its already a week but still my dog is very weak and gums very pale.

  8. I made a small piece of steak and onions for my dinner at 6:00pm. I gave my Cavalier a few little pieces of the steak but no onions. The flavor and juice of the onions were on the little pieces that she ate. About 11:00pm she started with diarrhea just once, now she is sleeping. I called my Vet and she said to just monitor her for any changes.
    Any suggestions?

    1. Hi Lorraine. While I wouldn’t recommend doing it again, the amount that you describe is extremely unlikely to cause any problems. Follow the advice and see your vet tomorrow if she isn’t back to normal. You can always call back if she gets worse.

  9. 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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