How onions and garlic harm dogs
All plants in the allium family contain sulfur compounds (such as n-propyl disulfide) that dogs can't break down well. These damage hemoglobin and the red blood cell walls, forming "Heinz bodies". The body then destroys the damaged cells. The result is hemolytic anemia: too few red blood cells to carry oxygen.
How much is too much?
| Dog weight | 0.5% of body weight in onion | About this much |
|---|---|---|
| 10 lb | 23 g (0.8 oz) | 0.2 medium onion · 2 garlic cloves |
| 20 lb | 45 g (1.6 oz) | 0.4 medium onion · 3 garlic cloves |
| 30 lb | 68 g (2.4 oz) | 0.6 medium onion · 5 garlic cloves |
| 50 lb | 113 g (4.0 oz) | 1.0 medium onion · 8 garlic cloves |
| 70 lb | 159 g (5.6 oz) | 1.4 medium onion · 11 garlic cloves |
| 90 lb | 204 g (7.2 oz) | 1.9 medium onion · 14 garlic cloves |
Garlic clove counts use the cautious end of Merck’s estimate (garlic up to 5 times as toxic as onion) and one clove weighs about 3 g. Japanese breeds such as Akitas and Shiba Inus may be more sensitive.
What to do
If your dog ate a significant amount within the last couple of hours, call your vet. They may make your dog vomit and give activated charcoal. Over the next few days, check your dog's gums (they should be pink, not pale or yellow) and watch for weakness or dark urine. Severe cases need hospital care and sometimes a blood transfusion.
Frequently asked questions
How much onion is toxic to a dog?
Onion toxicosis is consistently seen when a dog eats more than about 0.5% of its body weight in onion at once. That is around 2.4 oz (68 g) for a 30 lb dog, roughly half a medium onion. Repeated smaller amounts can also add up.
Is garlic worse than onion for dogs?
Yes. The Merck Veterinary Manual rates garlic 3 to 5 times as toxic as onion, and garlic and onion powders are more concentrated still, because the water has been removed.
How long does onion poisoning take to show?
Stomach upset may appear within a day, but signs of anemia (weakness, pale gums, fast breathing, red or brown urine) usually show up 1 to 5 days later.
Are cooked onions safe for dogs?
No. Cooking, frying or drying does not destroy the compounds that damage red blood cells. Gravy, stuffing, soups and baby food made with onion powder are common culprits.