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Q&A: Will My Cats Ever Get Along?

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Dr. Mark is a veterinarian. He works with dogs, cats, exotics, and livestock.

Chronic pain can lead to inter-cat aggression.

Chronic pain can lead to inter-cat aggression.

Is It Possible That My Cats Will Never Get Along?

"I have two female cats, both of which my husband and I adopted as strays: One is a big 17-pound Calico (Sharkie), and the other is a Russian Blue (Blue). Sharkie, being older and bigger, tried to bully Blue because she was smaller and younger. I intervened in their squabble one time, and that settled their differences. They still don't get along—they just co-exist and respect their territories.

A few years later, I adopted two male cats (they were brothers and could not be separated) and brought them home. My husband let them both out of the box when we got home. We never slowly introduced the new cats to the older cats, but they got along fine. The two male cats were about 3-months old, and we named them Tom and Jerry.

For three years, all the cats got along/co-existed fine. But something changed last year. I don't know what Tom did to Sharkie, but now Sharkie is so mad at Tom. Now Tom is always hiding and lurking around to make sure Sharkie is not around because she chases and bites him and he's scared. I feel like Sharkie would kill Tom if she could.

This has been going on for a while now, and I think Tom is suffering from extreme stress. He keeps on cleaning/licking and biting himself, to the point where his two hind legs are almost bald. I scheduled Tom to see our vet twice, but I had to cancel twice because I could not get hold of him. Once he suspects something is going on, he bolts and hides.

How can I get Sharkie to stop being so mean to Tom? I do not want to re-home him and his brother. Thank you." —Evelyn

There are several possibly reasons why Sharkie no longer gets along with Tom, but the first thing I would be concerned about is that she is in pain. She is a big cat and a senior—have you noticed that she is reluctant to jump up on the couch or scratching post area? She may be feeling bad because of arthritic pain.

It is really difficult to tell for sure how prevalent this problem is, but research has shown that anywhere from 28 to 82% of cats have behavioral changes due to pain. (1) Inter-cat household aggression can be one of those behavioral changes.

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Feliway for Behavioral Problems in Cats

Some behaviorists recommend that if there are any indications of pain, a cat should be treated for that problem even before behavior therapy.

If the physical and bloodwork are normal the behavioral therapy should start wtih Feliway, a pheromone that helps some cats with aggression toward their housemates. Even with the hormone, the aggression may not totally go away, but at least it tends not to escalate. (2)

Valium or Prozac for Aggressive Cats

That is about as much as we can hope for at this time. You can talk to your local veterinarian about putting her on a medication like Valium or Prozac to make her less aggressive.

I do not think Tom did anything to provoke this—it's more likely that he is just the victim. You may not like the changes in Sharkie if she is on medication, but Tom would surely appreciate it. If Tom were living in a group with Sharkie in the wild, he would most likely re-home himself.

I hope all goes well with them. A lot of stress changes we see in cats come about slowly, but it sounds like this has been going on for a while, so you should have her seen as soon as possible for Tom's sake.


(1) Mills DS, Demontigny-Bédard I, Gruen M, Klinck MP, McPeake KJ, Barcelos AM, Hewison L, Van Haevermaet H, Denenberg S, Hauser H, Koch C, Ballantyne K, Wilson C, Mathkari CV, Pounder J, Garcia E, Darder P, Fatjó J, Levine E. Pain and Problem Behavior in Cats and Dogs. Animals (Basel). 2020 Feb 18;10(2):318.

(2) DePorter TL, Bledsoe DL, Beck A, Ollivier E. Evaluation of the efficacy of an appeasing pheromone diffuser product vs placebo for management of feline aggression in multi-cat households: a pilot study. J Feline Med Surg. 2019 Apr;21(4):293-305.

This article is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from your veterinarian. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2022 Dr Mark

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