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Why is my cat with diabetes and hyperthyroidism so tired?

Updated On September 23rd, 2025

Pet's info: Cat | Mixed Breed | Female | spayed | 9 lbs

My cat has diabetes but recently she's developed a problem with her thyroid gland and has to take 2 tablets a day but since she's been taking these she's become very tired and miserable. I wonder if it is ok to treat her thyroid while she's on insulin and would a second opinion?

2 Answers

Most Helpful Answer

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Answered By Jennifer Summerfield, DVM CPDT-KA

Veterinarian, Certified Dog Trainer

Published on November 18th, 2016

Poor Willow! I'm sorry she hasn't been feeling well. Generally speaking, yes - it's perfectly fine for a cat to be on medication for hyperthyroidism as well as insulin for diabetes. These two illnesses are both common in older cats, so many cats are on treatment for both problems. But, it isn't normal for Willow to be acting tired and miserable since starting her thyroid medication - this indicates that something needs to be changed. Some cats get an upset stomach and don't feel well on the oral tablets, but may do better with a transdermal gel or other formulation. Other cats simply don't tolerate methimazole (the medication) well no matter what, so other treatment options may need to be discussed. In rare cases, we can see potentially serious side effects with this medication such as bone marrow suppression, which could also cause lethargy and weakness - so it would be a good idea to have blood work rechecked with your vet as well to make sure that this isn't the problem. I would recommend calling your vet today to discuss the issue and see what they would suggest as the next step.

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Other Answers

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    Answered By Sara Farmer, DVM

    Veterinarian

    Published on

    It is definitely okay to treat hyperthyroidism and diabetes at the same time. Hyperthyroidism can make cats hyperactive and irritable, so she may seem more 'tired' with her thyroid in the normal range but she shouldn't seem miserable. If she hasn't had full lab work performed recently this could help look for other potential causes of lethargy and a behavior change. I would bring up your concerns with your veterinarian and if you feel like your questions aren't being addressed make an appointment for a second opinion.

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