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My cat's hyperthyroidism: Methimazole side effects. What to do?

Updated on September 23rd, 2025

Pet's info: Cat | Mixed Breed | Female | spayed | 17 years old | 7.3 lbs

My 17 yr old cat has been diagnosed with hyperthyroidism. she was started on Methimazole chew treats and now refuses to eat them. I switched to the twist a dose ear Methimazole but if I give that to her daily like the vet suggested, all she does is sleep day and night. It seems to knock her out right after I apply it to her ear. then she starts vomiting her food. I am beginning to think we would be better off going with the radioactive iodine thing. what do you think?

1 Answer

Most Helpful Answer

Answered By Chad Brown, DVM

Veterinarian

Published on July 1st, 2018

Luv Bug is so very fortunate to have you as an owner. I am sure that you are one of the main reasons that she is going strong at 17 years of age. Kudos to you for your consideration and compassion for your pet.

In terms of hyperthyroidism in cats, there are only three real treatments on the market today. These are methimazole treatment, thyroidectomy surgery, and radioactive iodine treatment. It is believed in the veterinary community that radioactive iodine is the gold standard treatment today.

With the information you have provided, I can offer you a few possibilities for future treatment:

1. Perhaps you can get the math him is all in a tablet form to crush it into a fine powder and then mix it with any palatable substance that she likes and then squirt it in her mouth with a syringe. This, however, may cause some behavior problems because she may not like this either.

2. If you are willing to accept the costs and all of the different parts that go with the radioactive iodine treatment, I say go for it because the success rate for that specific treatment is excellent.

Thank you very much for your question and I know you will make the right decision on her behalf. Have a great day.

1Pet Parents found this answer helpful

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