The short answer: No.
The long answer: Otherwise known as bulb onion or common onion, onion is a widely popular vegetable of the genus Allium that is used to add flavour to dishes. Similar to garlic, this aromatic, layered vegetable contains disulfides and thiosulphates that can do irreparable damage to your cat’s body. Eating a large bulb of onion just once (about 0.5% of her body weight) or consuming small amounts regularly can cause your cat’s red blood cells to become fragile and burst. This can lead to conditions such as hemolytic anemia, Heinz body anemia, and methemoglobinemia.
What to do if your cat accidentally eats onion: Call your veterinarian to get advice on what to do as soon as possible. Monitor your cat closely in the next few days for any of the following signs: vomiting, blood in urine, weakness, high heart rate, panting, fever, loss of appetite, skin discolouration, and breakdown of red blood cells. Depending on the severity of the onion poisoning, your cat may spend a few days in the veterinary hospital and receive a blood transfusion.
In summary: Protect your curious cat from harm by storing, preparing, and disposing of onions properly. More importantly, refrain from feeding your cat table scraps that may contain onions. Even onion-flavoured food has been known to harm cats. Instead of onions, discover which human food cats can safely consume in our “can cats eat” category.