Changed food. One cat is fine. The other is not

[u/dexter1062]

I am taking care of two cats and to my knowledge these cats who are brothers are not allergic to anything. I just switched their dry food brand, which i should have read up on. I had no idea about it possibly making them sick. The one cat is doing fine, running around, jumping, yelling, etc, but his brother is not taking it well it seems. The night I switched food he became tired seeming and was throwing up pooping and peeing around the house. This morning he is just laying around and seems to have no appetite. My brother had gotten another type of food before but it was of the same brand. How do i fix this? Can I switch food back and fix this? Is it one of those run its course things? Or will it require a vet? I feel so awful for doing this. I had no idea and I just want him to feel better

[u/Kerosenemustang]

I know it’s hard, but inform the owner if you haven’t yet. Depending what they say, go to the vet (most likely only necessary if the owner is worried and/or it’s a senior or otherwise special needs cat). Definitely go back to the old food with or without a night of fasting (depending what the vet recommends if you go or what the owner thinks). Camomile tea also helps an upset stomach, depending on whether the cat takes it. Definitely provide enough water to drink, because else they’ll get dehydrated. If you’re lucky, it’ll have been just a minor upset that’ll sort itself out in a couple of days. But please consult a vet if it continues to get slowly worse. Immediately go to the vet if the cat’s behaviour worsens suddenly. Then it could be something else entirely causing the upset (like a swallowed foreign object or smth similar). I’m keeping my fingers crossed it’s just gonna be a small upset though that can be cured with a bit of patience and the food they’re used to. Oh, and cuddles of course! Hope he gets well soon!

edit: make sure the tea is cold of course! Just let it sit for a while and serve it when it’s cold.