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My senior cat has loose stools after Miralax. Is this normal?

Updated on September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Male | neutered | 16 lbs

13 year old cat had constipation. Vet advised Miralax. No longer has a formed stool--always a loose stool. Has problem been solved or is there still a medical issue?

2 Answers

Most Helpful Answer

Answered By Stacey Anstaett, DVM

Veterinarian

Published on July 9th, 2018

Most cats will not have a formed stool while on Miralax or any other stool softener. If the stools are quite loose, decrease the amount and/or frequency of Miralax.
You are correct in saying that lactulose is a sugar; however, it WILL NOT cause diabetes. Mammals are not able to break the lactulose molecule down and it is not readily absorbed in the GI tract. It stays in the GI tract, which helps draw water into the GI tract---this is how it has a stool softening effect.

Regarding your question for "is there still a medical issue," it sounds like the constipation is resolved, however, there could be an underlying motility issue in the colon that will require continued need for Miralax or other ongoing treatment. Another concern in older cats is kidney disease; we occasionally find that constipated cats have chronic kidney disease.

I hope that answers your question!! If not, feel free to request a consultation where we can exchange information back and forth.
Thanks for asking Petco Pet Education Center, formerly Petcoach!

1Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Laura Johnson VMD
Veterinarian
Hi, thanks for using Petco Pet Education Center, formerly Petcoach!

It is hard to tell with out an exam and belly X-ray. Sometimes when constipated cats strain they will pass softer stool past the hard stool. If it is a large volume of loose stool then maybe it is solved. If that is the case I would decrease the amount or frequency of the miralax. If you are not sure I would have him rechecked by your Vet to see if he is still constipated and needs more aggressive medications like Lactulose and a prescription diet like Royal Canin Fiber Response. Constipation in an older cat is a sign of something else like kidney or intestinal disease.

I wish Siba the best
0Pet Parents found this answer helpful

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