My cat ate an onion. How long until symptoms show and what are they?
Updated On September 23rd, 2025
Pet's info: Cat | Mixed Breed | Female | spayed | 11 years and 10 months old | 9 lbs
Hello, my 11 year old female cat may or may not have eaten a piece of an onion off of the floor. The only reason I think it’s an onion is because my housemate was doing something with onions. By the time I saw her chewing and ran over to her to her to see what it was, she had already swallowed it. Suppose it was a piece of an onion, how long would it take for symptoms to show for onion poisoning? Also, what are the symptoms? She seems fine so far. This happened about 20 to 30 minutes ago.
2 Answers
Most Helpful Answer
Published on February 27th, 2018
It depends on the size of the piece of onion, but this normally would not be enough to cause toxicity, so I wouldn't worry too much. The biggest concern with onion toxicity is that it destroys the red blood cells. This takes a few days to happen though. You may notice vomiting when they first eat the onion, but other signs of toxicity won't be obvious until 2-5 days later. Signs of onion toxicity are a dramatic decrease in activity and pale gums. If you notice this, then it's best to have Tabbi seen by a vet as soon as possible. Otherwise, if she is completely normal after a week, then I would not worry about her having any problems related to the onion. I hope that helps and all is well with Tabbi.
1Pet Parents found this answer helpful
Related Answers from Veterinarians
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Published on February 13th, 2018
Hi, thanks for using Petco Pet Education Center, formerly Petcoach! Onions and garlic toxicity causes oxidative injury to the red blood cells causing anemia. So the symptoms would mimic anemia: weakness, depression, pale gums, jaundiced, abnormal colored urine, high heart rate, not eating, increased respiratory rate. The cat could have transient upset tummy signs before the other signs occur. Signs usually show up with in 7 days or 1-2 days if the animals ingested a very large amount, though the damage to the red blood cells starts with in 24 hours. I hope this helps!
1Pet Parents found this answer helpful
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