Symptoms and Treatment of Onion and Garlic Poisoning

ImmunityDiseasesMeongsiljang Veterinary Advisory Board

Onions, garlic, and other allium-family plants can destroy red blood cells in dogs and cats, leading to hemolytic anemia. We’ve summarized everything you need to know, including poisoning symptoms, emergency first aid, treatment processes, risky foods, and prevention tips.

What is Onion and Garlic Poisoning?

Dogs and cats near scattered onions and garlic on the kitchen floor

Onion and garlic poisoning is a toxic condition caused by organosulfur compounds found in Allium plants, which destroy red blood cells and lead to anemia. The most critical point to remember is that toxicity can accumulate even if small amounts are consumed over several days, rather than in a single large ingestion. If you notice any of the following symptoms—vomiting, lethargy, pale gums, or dark urine—seek immediate veterinary care. Both dogs and cats are susceptible, but cats are particularly vulnerable because their hemoglobin is more prone to oxidative damage, meaning they can become poisoned by smaller quantities.

Why is it Dangerous? Causes and Mechanisms of Poisoning

Onions, garlic, chives, scallions, and other Allium species contain organosulfur compounds. These substances cause oxidative stress in the body, damaging hemoglobin within red blood cells. The damaged hemoglobin forms abnormal inclusions called Heinz bodies, leading to the destruction of these red blood cells and resulting in hemolytic anemia. Toxicity remains present not only in raw onions but also in cooked onions, onion powder, garlic powder, and sauces or broths containing onions. Cooking, drying, or processing into supplements or powders does not eliminate the toxicity. Both dogs and cats can suffer from red blood cell damage, but cats are particularly vulnerable, with blood toxicity potentially occurring after ingesting as little as 5 grams per kilogram of body weight. Additionally, garlic can be up to five times more toxic than onions, requiring extra caution. Since the exact toxic dose varies depending on the individual and circumstances, it is safest to consult a veterinarian if you are unsure of the amount ingested or if your pet has consumed even a small amount.

Suspect Onion and Garlic Poisoning if You See These Symptoms

Symptoms of onion and garlic poisoning typically appear in two phases: gastrointestinal signs followed by signs of anemia, with a noticeable time gap between them. Gastrointestinal symptoms such as vomiting and diarrhea can occur within a day of ingestion, whereas symptoms resulting from anemia often take several days to a week to manifest. If you notice any of the following signs, seek veterinary care immediately.

Vomiting and diarrhea: These are the earliest gastrointestinal signs, usually appearing shortly after ingestion.

Lethargy and decreased appetite: As anemia progresses, your pet will become weak and lose interest in food.

Pale gums and tongue: The destruction of red blood cells causes the mucous membranes to turn pale.

Dark brown or red urine: Hemoglobin from destroyed red blood cells is excreted in the urine.

Rapid breathing: A shortage of red blood cells to carry oxygen causes labored or fast breathing.

Increased heart rate: The heart beats faster to compensate for the lack of oxygen in the body.

A lethargic puppy lying down with pale gums

Go to the Vet Immediately if You See These Symptoms

If your pet’s gums have turned pale, their urine is dark brown or reddish, or they are panting heavily, anemia has likely progressed significantly. If you know they have ingested onions or garlic, seek veterinary care immediately, regardless of how much time has passed. In the early stages after ingestion, a veterinarian can induce vomiting or administer activated charcoal to reduce the absorption of the toxins. Do not attempt to induce vomiting at home with salt water or other methods, as this can be dangerous; always follow your veterinarian’s guidance.

Diagnosis at the Veterinary Clinic

The veterinarian will first check for any history of onion or garlic ingestion and assess the severity of anemia through blood tests.

Blood smear test: A microscope is used to check for the formation of Heinz bodies in red blood cells and any changes in red blood cell shape (eccentrocytes).

Complete blood count: Red blood cell count and hematocrit levels are measured to determine the severity of the anemia.

Urinalysis: The urine is tested to see if hemoglobin is present.

Biochemical profile: Other organs, such as the liver and kidneys, are evaluated for any signs of damage.

How is Treatment Conducted?

There is no specific antidote for onion or garlic poisoning, so treatment focuses on managing symptoms.

Inducing vomiting: If the ingestion was recent, a veterinarian may administer medication to induce vomiting. This is most effective in the early stages before symptoms appear.

Intravenous fluid therapy: Fluids help correct dehydration and maintain blood flow to the kidneys, preventing kidney damage caused by hemoglobin.

Blood transfusion: If red blood cell counts drop to dangerous levels, a blood transfusion may be necessary.

Oxygen therapy: In cases of severe anemia causing breathing difficulties, supplemental oxygen is provided.

The prognosis is generally good if treatment begins early. However, if severe anemia is present, hospitalization for several days and follow-up tests to monitor red blood cell counts may be required.

A puppy receiving intravenous fluid therapy at a veterinary clinic

Foods That Hide Onions and Garlic

Onions and garlic are staples in Korean cuisine, so owners often unknowingly feed them to their pets. These are especially dangerous foods to watch out for.

Jajangmyeon (black bean noodles) and curry: These dishes contain large amounts of onion.

Bulgogi and galbi marinades: Onion juice and minced garlic are key ingredients in the seasoning.

Doenjang-jjigae (soybean paste stew) and kimchi-jjigae (kimchi stew): Even the broth is risky if it contains green onions or garlic.

Hamburger patties: Onions are frequently mixed into the meat.

Garlic bread and garlic sauce: The high garlic content makes even small amounts dangerous.

Baby food and nutritional porridge: Human baby food may contain onions or garlic.

The mindset of "just a little bit won't hurt" is the most dangerous assumption you can make.

A dog gazing up at a table set with Korean dishes like bulgogi and jjajangmyeon that contain onions.

Prevention and Management Tips at Home

Preventing allium plant poisoning requires careful daily management.

Immediately clean up any dropped ingredients while cooking: If you drop an onion while chopping, pick it up right away.

Do not share human food: Most seasoned dishes contain onions or garlic.

Check the ingredient labels on treats and supplements: Some pet products may contain garlic extract.

Use locking mechanisms on trash cans: Pets may dig through garbage to find onion or garlic peels.

Inform all family members: Accidents often occur when children or elderly relatives unknowingly feed these foods to pets.

Cats and Certain Breeds Are at Higher Risk

Cats are far more susceptible to Allium plant toxicity than dogs. Because feline hemoglobin is about two to three times more sensitive to oxidative damage than that of other animals, even tiny amounts can trigger Heinz body formation and severe anemia, so please exercise extra caution. Among dogs, certain purebreds such as the Japanese Akita have been reported to be more vulnerable to Allium toxicity. If you own one of these breeds, be especially careful with foods containing Allium plants, and consult your veterinarian immediately if your dog ingests even a small amount.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is it dangerous even if my pet only ate a small amount of onion?

Even small amounts, when consumed repeatedly relative to body weight, can lead to toxic buildup. Cats are especially vulnerable and can become poisoned by very small quantities. If you’re unsure about the amount ingested, the safest course of action is to call your veterinarian for advice.

Are cooked onions or garlic safe?

No, that’s not the case. The toxic organosulfur compounds in onions are not destroyed by cooking methods such as grilling, stir-frying, or boiling. Even broths containing onions are dangerous.

I’ve heard that garlic helps prevent parasites. Is that true?

This is an unproven home remedy. In fact, garlic is up to five times more toxic than onions and should never be given to pets. A study by Lee et al. (2000) confirmed that garlic extract damages red blood cells in dogs.

It’s been a day since my pet ate onion, and they seem fine. Can I skip the vet visit?

Gastrointestinal symptoms such as vomiting and diarrhea can appear within a day of ingestion, but signs of anemia may not show up for several days to a week. Even if your pet seems fine now, anemia could still be progressing, so it’s important to have a blood test done at the clinic.

Is it safe to induce vomiting at home?

Absolutely not. Inducing vomiting with salt water poses a risk of sodium poisoning. Vomiting should only be induced safely by a veterinarian at an animal hospital using appropriate medication.

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References

[1] Lee KW, Yamato O, Tajima M, et al., Hematologic changes associated with the appearance of eccentrocytes after intragastric administration of garlic extract to dogs, American Journal of Veterinary Research, 2000

[2] Cope RB, Allium species poisoning in dogs and cats, Veterinary Medicine, 2005

[3] Yamato O, Maede Y, Susceptibility to onion-induced hemolysis in dogs with hereditary high erythrocyte reduced glutathione and potassium concentrations, American Journal of Veterinary Research, 1992

[4] Blackwell's Five-Minute Veterinary Consult Clinical Companion, Small Animal Toxicology, 3rd Edition

[5] Clinical Medicine of the Dog and Cat, 4th Edition

[6] Plumb's Veterinary Drug Handbook, 10th Edition