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Why isn't my senior hyperthyroid cat gaining weight and vomiting?

Updated On September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Male | neutered | 15 years and 4 months old | 9 lbs

My 14+ year old male cat has lost weight. It was determined that he has hyperthyroidism. So he has been an a hyperthryoidism RX since April. He is eating very well but doesn't seem to be gaining weight. Also he is drinking a good amount of water and voiding well. About every other early morning he has been throwing up a little of his fur but mostly water. Should I be concerned?

4 Answers

Most Helpful Answer

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Answered By Sara Farmer, DVM

Veterinarian

Published on September 24th, 2018

If JR’s thyroid hormone has been rechecked and is normal it is unlikely that his lack of weight gain is related to thyroid disease. If his T4 has not been rechecked then this is probably your best first step since all of his symptoms could be attributed to hyperthyroidism. He could also have inflammatory bowel disease, kidney disease or even diabetes in addition to thyroid disease. I would recommend making a recheck appointment with your vet.

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Other Answers

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    Answered By Dr. Elizabeth

    Veterinarian

    Published on December 5th, 2019

    Other conditions which could cause similar symptoms include kidney disease, IBD, food allergies, liver disease or it could still be hyperthyroidism pending what test was run. If only a total T4 was run, some cats will test normal even though they truly have hyperthyroidism. If the vet strongly suspects Hyperthyroidism, ask about running a full thyroid panel which could be more sensitive. I hope this helps and please feel free to post any additional questions.

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    Answered By Linda G, MS, DVM

    Veterinarian

    Published on September 23rd, 2019

    Hello. While the thyroid gland can be enlarged with hyperthyroidism, it is not always obvious. The best way to test for this is through a blood test. Older cats can also be prone to kidney problems, & of course, cancer. Some things can be managed fairly easily by you, but find out first what might be going on with Chloe, & then have a frank discussion about quality of life for her. 17 years is a long life for a kitty. You have obviously cared very well for her. I hope you can enjoy each other for at least some time to come. Thanks for using Petco Pet Education Center, formerly Petcoach.

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    Answered By Jennifer Summerfield, DVM CPDT-KA

    Veterinarian, Certified Dog Trainer

    Published on February 11th, 2019

    Hi there. Yes, the symptoms you are describing could be consistent with hyperthyroidism. Increased appetite along with weight loss can also be caused by diabetes, an intestinal absorption issue, or a number of other things. Your cat will need blood work to help diagnose the problem, so I would recommend taking him to the vet for an exam as soon as you are able to. He/she can get him started on appropriate treatment once a diagnosis is made.

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