Excesssive Vomiting After Cat Meets New Kitten. Help!!!

Hanna M

TCS Member
Sep 23, 2022
Hi - I made an account just to add to this thread to help others who were desperately googling this issue. There is a lack of resolution for many stories, so I just wanted to say what helped us. I experienced the exact same thing with my 4.5 year old cat Sushi, about 10 days after introducing a new 6-month-old kitten Bento. We thought we did a by the book introduction, with isolation first, then room swapping, then brief supervised visits, then letting Bento roam around longer during the day and still sleep in her own room during the night. Feliway running the whole time, tons of treats and love, and the cats were already starting to sit next to each other and it was pretty peaceful, so we decided it is ok for us to let Bento join the family and sleep with Sushi and us during the night.

The following day Sushi started vomiting profusely, terrible diarrhea, can’t keep anything down and is just overall lethargic/hiding. After 2 days of that, I noticed blood in her diarrhea and we took her to the ER during the night. Long story short, this whole thing lasted for 5 days. 2 ER visits, a vet visit, a ton of tests that all came back clean and $3000 later, what ended up helping Sushi is a night on IV fluids and separating Bento back into her base camp again. She started eating and keeping things down on day 6 after coming back from the hospital, and had her first normal poop in a week on day 7.

Since every possible physical cause was ruled out and Bento has a clean bill of health too, we had to accept the explanation that it was all stress related. It took me a long time to come to terms with that explanation, because it basically means that I did this to my baby girl and it just feels awful as a pet parent who was just trying to do right by their baby and give them a friend. It was extremely validating to find this thread and see I am not the only one to have such an extreme reaction to stress, because I watched a million cat introduction videos and not a single one of them even mentioned a possibility of a cat getting this ill to stress.

In hindsight, we believe what happened is that we went too fast for Sushi with the introduction. It was a mistake to let Bento sleep in the same room as us only 10 days in - and another thing that possibly could have served as a precipitating event to trigger massive stress is that we bathed Bento the night before it all started (shelter kitten formerly on the streets who stank like hell and really needed just this one bath after her spay scar healed). It was a traumatic experience for all involved, including Sushi because she was vocalizing and acting really distressed while it was happening. Not sure if it had anything to do with the vomiting, but it probably didn’t have an already stressed system.

Anyway, just wanted to share what happened with us to help others. We are not giving up on Bento because she is ours too and we love her, but we massively backed off and started a slow re-introduction now that Sushi is eating and pooping again. We are increasing the amount of time they spend in contact during the day, but will keep them separated during the night for a long while, since Sushi doesn’t seem to be able to fully relax in Bento’s presence and that full relaxation time is critical for health and immune system.

Another tip we discovered helped us that I haven’t seen anywhere else is that getting a second of everything seems to help with jealousy. We got a second cat tree, a second heated bed, a second basket on the table, etc. Bento went right for all of Sushi’s things and it seemed to really distress her, but now they each have one of their own, and I think it’s helping her feel a little less like she is losing territory and a little more like she now has 2 of everything. Good luck with your kitty - hope this helps!


TCS Member
Alpha Cat
Apr 29, 2022
Not sure whose still around here, but in my experience many vets will let you know that it's stress. However:

1. With cats it's always either a. This is very serious and urgent or b. This is nothing at all to be concerned of and BOTH are the same symptom set.

2. It's important to rule out those serious things or you're going to get some VERY angry clients and lawsuits VERY fast.

I recommend going to a cat specific vet if possible. I usually find that they can better judge if you have a few days to act conservatively and monitor. They provide what to watch for to bring them back.

It's very important with cats with health histories to go slowly with introductions. You have to plan to do this over several months.

My senior cat has FLUTD (stress disorder) and I have successfully introduced cats to him without flare ups. It is EXTREMELY important to follow the steps slowly and take the time out to do activities that calm your stressed resident cat: play, treats, love, trips to the balcony or terrace, new enrichment activities and most importantly, extra water added to their food during the stressful period. Do not push your resident cat to eat their meals next to the door of the new cat as suggested in Jackson Galaxy's videos or similar. Skip that step and do others. However, offer many treats while they see the new cat.

Lastly, the older cats may have gotten a cat cold.or cat flu due to the season and/or their contact with new cats. It usually clears up in a few days to two weeks. It's VERY common for cats who don't go to the vet frequently as their immune systems may not be as strong as they haven't encountered as many things. It's best to get your resident cats their yearly cat cold/flu vaccine before bringing a new cat home or if you'll have frequent contact with cats outside your home.

I would ask the vet for some prescription chicken and rice (digestive) food for some time and what their l-lysine dosage would be. It works for some and is worth a try. For my cat at 6 lbs it was 1/8 tsp per day.

It would be a shame as well to have put your cats through this stress, for nothing (aka giving them back). And it would also cause issues for the new cats. I hope anyone reading this can consider slowing down and or rolling back their introductions so that the issue can be resolved.

Cat introductions for stressed cats should take longer than 3 months at a slow pace and can take up to a year to be fully meshes 24 hours a day. Do not hesitate to continue having a few hours a day of separation to keep stress levels lower for as long as needed.
There's some excellent advice from Hanna M Hanna M above too.