5 month old female kitten will not use litter box

I adopted a 5 month old female kitten, she is fixed, up to date on all shots and in good health. She used the litter box at the shelter and now that she has a home she won't use the litter box.

I have 2 other cats a 12 year old and a 1 year old. I also have 2 litter boxes that are cleaned everyday. I don't want to have to take her back to the shelter, but I am at my wit's end.

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My Thoughts:

Thank you for adopting another cat! I'm sorry to hear that your cat is having trouble.

My suspicion is that since she was using the litter box but now is not, that she is having problems due to the transition.

It's vital that the transition from the shelter to the new home be done as smoothly and stress-free as possible.

This transition includes a strict quarantine period and an extended period of isolation. You didn't mention that you've done this so I'll review that here and give you some further reading.

This isolation is partly to protect your resident cats from illness and to protect all the cats from having behavior issues and ensure they get along.

During this time, the new cat is kept in isolation in a "safe room." This is where litter box habits are established and "corrections" are made if necessary.

Then, over time, a slow introduction is done so that the new cat and the old cats can accept each other and learn to share resources and space.

If this process is not followed, unpredictable results, including litter box problems, behavioral issues, and aggressive behavior among the cats is very possible.

Did you provide a safe room and a period of isolation (several days to several weeks) for the new kitten?

If not, you need to follow that process. I've outlined this process well regarding introducing a stray cat into the house but it applies to any new cat.

Along with Feliway, isolation was the solution to this reader's problem with her cat post-surgery. I hope that success story provides some encouragement.

If you just brought her home, then she should be in her safe room in quarantine. If she's been let out of her safe room, place her back in there until her litter box habits are golden.

If you did not provide a safe room and quarantine/isolation period, then you've skipped a vital step.

I'm curious to know if this was all explained to you at the shelter or by your veterinarian. If not, clearly I still have much work to do as this information should be freely available and required reading by all who adopt a cat.

We haven't even gotten into whether this is restricted to urination or defecation or both, or whether or not it's marking, but isolation comes first. Always.

I hope that helps. Please let me know in the comments where we stand with this as we need to get your kitten back on track.
-Kurt