Hyperthyroidism in my cat

My cat was sick all the holiday weekend, vomiting frequently. I got her to the vet first thing Monday and they said she has hyperthyroidism. She’s 13. They put her on oral Methimazole but she pukes that up when we give it to her, and she pukes every time she eats. Waiting for the vet to open now to call them back but thought the COTH folks might give me some advice. If she can’t hold the meds down what can we do?


You can treat the nausea with cerenia or zofran. Further work up might be needed to figure out why she’s vomiting, though, as that’s not a typical symptom of hyperthyroidism (I don’t think? It’s been awhile!)

Going forward, there is a transdermal prep of methimazole, although you do have to be very careful that it doesn’t transfer to you, and some vets won’t prescribe it due to that risk (mine would not.)

There is also radioactive iodine treatment, which would be curative, but they like to see them do well on methimazole before considering that.

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@Simkie thanks. Just got a call back from the vet. Bringing her in for the cerenia shot in a couple of hours. And the vet said he would prescribe the transdermal methimazole. And waiting for a case of Thyroid Hills Science Diet food delivered on Friday. If she quits throwing up, we can stay with the liquid methimazole. Poor girl, she feels so bad.

The American Academy of Feline Practitioners has published guidelines for the management of hyperthyroidism in cats. It’s an excellent resource and you can access it here: https://catvets.com/guidelines/practice-guidelines/feline-hyperthyroidism

I’ve had two hyperthyroid cats, and both were treated with radioactive iodine. Both were cured of their hyperthyroidism. I tried methimazole on one cat but she couldn’t tolerate it, and that’s why I went with the radioactive iodine. This is expensive up front, but long term it can be cheaper than methimazole because you don’t have to keep paying for vet visits, medicine, and lab tests. The really nice thing about radioactive iodine is that it cures the disease rather than just masking it. No more pills, no special diet, no more sick cat.

Simkie has some good comments–treat the nausea and see if that helps and maybe try the transdermal gel. You can wear gloves when you apply it to keep from absorbing it through your skin. I think the new guidelines no longer recommend a methimazole trial before going to radioactive iodine.

Let us know how your cat is doing. I feel for the little girl.

@OzarksRider Thank you for this information. I will talk to my vet about it. She’s only 13. I’ve had 2 live to over 25 - so maybe the radioactive iodine is the way to go.

The cerenia shot at 3 today really seemed to help. So she is home and we have more pills for the nausea for 8 days. At 6 today we put the liquid methimazole on some wet food and she ate it right up. Has not puked since 10 this morning. Hopefully we turned a corner. Thanks for your help COTH.


We also did radioactive iodine for one of our cats and I would for sure do it again! It was a bit of a pain storing his waste for 6 months (I think) before tossing it, but was the worst. His thyroid levels have been perfect since the treatment

Oh and the radioactive iodine seems expensive, but when we figured it out it cost less then 2 years of medication. That was over 5 years ago so it definitely ended up being more affordable

OP, glad to hear your kitty is doing better. I have my hyperT cat on a twice daily pill which he tolerates well. He is also diabetic. he has gained some weight and feels so much better than he did before. It’s a very manageable disease once you get the kinks worked out. Hope she continues to improve.

I did the radioactive iodine and would do it again. I think my cat was about 11. At the time the alternative meds were only in pill form and I felt that the money I spent on the treatment was well worth not giving pills to a cat for the rest of her life.

She made it through the night with no more vomiting and was very hungry this morning and purring like crazy. She is a much happier kitty today.