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Home > Ask A Vet > My Dog Ate Onions – What Should You Do (Vet Answer)

My Dog Ate Onions – What Should You Do (Vet Answer)

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Dr. Joe Mallat

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

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For many people, the aroma of onions or garlic simmering in a pan can be hard to resist. We also know how well they go in burgers, soups, pasta, and other common meals. That aroma is tempting for dogs, too, whose sense of smell is at least 10,000 times better than ours. Unfortunately, onions and other members of this herb family are very toxic to dogs and cause life-threatening anemia. If your dog has ingested onions (particularly if it’s a large amount), urgent veterinary attention is warranted. 

This article will explore onion toxicity in dogs, while answering some questions you might have about why it’s so bad and what can be done about it.  


Why Are Onions Bad for Dogs?

There is a very destructive component of onions (and similar species) that causes red blood cells to burst. This component is an organic sulfide molecule that causes oxidative damage to red blood cells—think of this as the opposite of antioxidants. This results in anemia, or a reduced number of red blood cells in the body. Red blood cells are vital for carrying oxygen around the body, so when dogs ingest too much onion and become anemic, different tissues in the body do not receive enough oxygen. This can be life-threatening. 

It is not just onions that can cause anemia in dogs. Onions are part of a family of plants called the Allium species, which also includes leeks, chives, garlic, and shallots. All members of the Allium species are toxic to dogs and capable of causing severe anemia. 

red onions on wooden table
Image Credit: Bukhta Yurii, Shutterstock

What Are the Signs of Onion Toxicity?

Initially, onion ingestion may cause no signs of illness at all. Some dogs will have gastrointestinal inflammation or “gut upset” on the first day following ingestion, resulting in vomiting, diarrhea, and sometimes abdominal pain.

Anemia following onion ingestion can take days to develop.

Signs to look for:
  • Weakness and lethargy
  • Reluctance to exercise
  • Labored breathing
  • Pale gums
  • Dark/discolored urine

How Much Onion is Toxic to Dogs?

In general. data suggests that as little as half a percent of a dog’s body weight in onions can cause toxicity. As an example, a 20-pound dog would only need to eat 1.5 ounces of onion to suffer its toxic effects. 

The amount of onion required to cause toxicity in dogs seems to be variable. While some dogs may tolerate a tiny amount of onion without any issues, other dogs appear much more sensitive to its effects. Cooked or rotten onion appears to be just as toxic as fresh onion. Additionally, some Japanese breeds of dog such as the Spitz appear to be particularly vulnerable to the effects of onions due to unique genetic factors.

How Can Onion Toxicity Be Diagnosed?

Onion toxicity can be diagnosed using a combination of history-taking, physical examination, and several blood tests. This will include a total red blood cell count, as well as an examination of red blood cells under the microscope to look for physical (“oxidative”) damage. Sometimes, imaging studies such as X-rays and ultrasound may be required to rule out other potential causes of anemia. There is no specific blood test to check for the presence of onion in a dog’s system. 

How Is Onion Toxicity Treated?

This depends in part on how severe the signs of illness are. If only a small amount of onion was ingested, resulting in vomiting and diarrhea, but the risk of anemia is deemed low, management at home may be warranted. This may involve activated charcoal, anti-nausea medications, and probiotics.

Dogs experiencing anemia due to onion ingestion require more intensive and aggressive treatment. This may include fluids via a drip to correct dehydration, blood transfusions, oxygen supplementation, supportive medications (as above), and monitoring at a vet hospital. 

great dane dog admitted in the pet hospital with good care of veterinarians
Image Credit: Jeab Ploykrachang, Shutterstock

My Dog Just Ate Onions – What Should I Do?

If your dog has just gotten into some onions, or if you’ve fed them to your dog unaware of their potential harm, arrange an urgent visit to your veterinarian. Vets will often give dogs medication to make them vomit, which should rid the stomach of onions and prevent the risk of anemia developing in a few days.  If your dog ate onions a few days ago and is now showing signs of being unwell, you should also arrange an urgent visit to your veterinarian, as diagnostics and treatment may be required. 



Dogs are very susceptible to onion poisoning, and the anemia caused by onions can be life-threatening. Thankfully, vets can induce vomiting early to get rid of the onions from the stomach; treatment for anemia is also possible and usually gets dogs back into good health. As always, early veterinary intervention gives your canine companion the best chance of a positive outcome. 

In the meantime, keep any onion-containing meals away from your dog, and if they like vegetables, consider cucumber or carrots instead. 

Featured Image Credit: Shutterbug75, Pixabay

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