Why are onions and garlic toxic to pets?
Alliums (onion, garlic, leek, shallot, chives) contain organosulfur compounds that damage red blood cells and cause Heinz-body hemolytic anemia. The effect is dose-dependent but can be delayed by 1–5 days, which makes it easy to miss.
Cats are more sensitive than dogs. Powdered forms are concentrated — a teaspoon of onion powder can be a serious dose for a small dog.
About the dose levels
Reference: eating more than ~0.5% of body weight in onions (~5 g/kg) can cause clinically significant red blood cell damage in dogs; garlic is roughly 2–3× more concentrated. This tool estimates onion-equivalents and is intentionally conservative.
Reference: eating more than ~0.5% of body weight in onions (~5 g/kg) can cause clinically significant red blood cell damage in dogs; garlic is roughly 2–3× more concentrated. This tool estimates onion-equivalents and is intentionally conservative.
Symptoms of onion-garlic poisoning
- Initially: mild stomach upset, drooling
- 1–5 days later: weakness, pale gums, lethargy
- Rapid breathing or elevated heart rate
- Dark or brown urine (severe hemolysis)
- Collapse in severe cases
What to do right now
- Call your vet for any meaningful amount — even before symptoms.
- Do not induce vomiting unless directed (it may be too late to help and can cause harm).
- Mention powdered forms too — they are much stronger by weight.
- Your vet may run blood tests to check red blood cell count over several days.
If your pet is already showing symptoms, don’t wait for a calculator result — call your vet or the ASPCA Poison Control center (888) 426-4435 immediately.
Sources & further reading
- ASPCA Animal Poison Control — pet poison database & dosage references
- Pet Poison Helpline — toxicology triage guidelines
- Merck Veterinary Manual — toxicology monographs
- Vets Now (UK) — emergency toxicosis guidance