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.
Signs to watch for
- 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 shows any of the signs above, go to the nearest emergency vet now and call ahead.
For a dose worked out against your pet's weight, use the Onion & Garlic Toxicity Calculator.