Can dogs eat onions?
Toxic. No. Onions and every other allium damage red blood cells and can cause hemolytic anemia several days after the meal.
How much is dangerous?
Merck notes that concentrated forms — dehydrated flakes, powders, dried soup mixes — are the usual cause, and that garlic is 3 to 5 times more toxic than onion by weight. Cooking does not reduce the toxicity.
Why it does harm
Sulfur-containing oxidants, released when allium tissue is chopped, cooked or chewed and by gut microbes, oxidize hemoglobin. The damaged hemoglobin clumps into Heinz bodies and the red cells are destroyed, producing hemolytic anemia.
What to look for
- Vomiting and diarrhea in the first hours
- Weakness, pale or yellow gums, and collapse days later
- Rapid breathing and rapid heart rate
- Red or brown urine
Timing. Digestive upset can be immediate, but the anemia typically appears several days after eating.
What to do
- Call your vet with the type of allium and the amount, remembering that powder is far more concentrated than fresh.
- Mention any packaged food involved: bouillon cubes, baby food, gravy and sauces are the usual hidden sources.
- A normal-looking dog on day one does not mean it is fine. The blood picture is what matters, and it develops later.