How long after eating onion does a dog get poisoned?

Dogs eating onion easily get acute poisoning, with obvious symptoms usually appearing 1 to 2 days after eating. If the dog shows no abnormality 3 days after eating onion, it means the amount ingested was small and the toxicity low, with little effect; the body will slowly metabolize the toxin.

But if the dog ate a lot of onion or shows red or reddish-brown urine after eating, the owner must take it to a veterinary hospital for treatment as soon as possible.