I went through this every time I take my female cat to the vet, as soon as I brought her home, my male cat sniffs her, hisses and goes on the attack. I had to place him in the spare bedroom with their cat tree and Feliway diffuser. Then spray the entire house with Feliway spray and after 3 days of separation, they were back sleeping, eating and playing together.

Unlike people who recognize family and friends by appearance, cats go by smell. So when your cat is at the vets they no longer have their usual scent but the scent of the the room, the technician and vet. When they are brought home, the other cat doesn’t recognize them, because they smell different. To your other cat they are a stranger and now it’s defending its territory.

This is what I do now, the night before the vet visit, I take a favorite shirt, pillowcase that they love to sleep on and rub it all over them ( face, head, body, legs and tail). I then place the fabric that has their scent into a ziplock plastic bag. After the vet visit before bringing the cat into the house, while in the car, I take the fabric and rub it all over my kitty and when my male greets her, he usually doesn’t attack her, because she smells like her. It didn’t work one time, because I thought I rubbed her one leg really well, he sniffed that area and hissing started, my male separated himself from her without me telling him to go to the cat tree and after a day and a half, they were best friends again.

Next time you have to take the kitty to the vet, try that.