I am at my wits end. My 15 year old cat has been diagnosed with hyperthyroidism. First she was on the mentimazole but didn't like it and peed everywhere so we stopped that and put her on the thyroid pill.

She had a bad reaction to that and started throwing up everything including water, so we stopped that and put her on the Hills Y/D food. That didn't go well as she stopped eating it within two weeks and would only eat a couple bits of the kibble when she was starving.

Our vet then put her on the Hill Y/D canned food but she had a reaction to it. After eating it, and yes, she did eat it but after eating it she could barely walk. While on both the dry and moist Hills food, she became very lethargic and slept all the time which led to her becoming dehydrated. She wasn't drinking because she was always sleeping.

Does anyone know of a pet store food that it low in iodine?

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    Was the problem with methimazole specifically the pill? There's a topical version that worked well for one of my hyperthyroid cats. The lethargy and dehydration sound like something else, though, not hyperthyroid. Oct 29, 2017 at 2:27
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    I know this sounds like a very stupid question, so forgive me, but was your cat was for sure tested for hyperthyroidism? Or was it a diagnosis based on symptoms? I will do my best with this, but want to make sure she had a panel test run concluding the diagnosis first. Thanks
    – Christy B.
    Oct 29, 2017 at 3:40

2 Answers 2


There are 4 primary treatments for hyperthyroidism. It sounds like you have tried two of them, the other two may or may not be appropriate or available to you based on your location.

  • Medication: Methimazole or carbimazole. The former is usually a tablet, but can be compounded into a transdermal form to apply to the ear (very popular). Ask your vet about other compounding options. If the cat goes off the medication, the hyperthyroidism will return.
  • Diet: Hill's y/d diet is low in iodine, still a relatively new product and I am not aware of any other companies that have a prescription thyroid diet. The diet has to be strict (no other foods or treats). It may take several weeks before you see significant clinical effect. Clinically I have not had great results with y/d diet alone, certainly some effect but not the level of thyroid control that methimazole can achieve.
  • Radioactive iodine: This is the gold standard treatment. The cat receives usually just one injection of radioactive iodine (I131) which kills the proliferative thyroid cells. Curative in the vast majority of cases.
  • Surgery: Removal of the thyroid gland is sometimes done (less frequently now). Risks of side effects including hypothyroidism and hypoparathyroidism.

Radioactive iodine is one of the most expensive options, but you have to bear in mind that it is a one-time cost compared to a distributed cost over possibly years of medical or dietary management.

Cats with hyperthyroidism commonly have other concurrent disease, especially kidney disease. If your cat is lethargic, very low energy, and inappetant, it is likely that there is something else going on (I highly doubt it is just the food that is causing this). Please see your vet as soon as possible.

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    I had a hyperthyroid cat whose pre-radioactive-iodine T4 was 70 (!) -- normal is ~1.5-4 -- and they weren't sure a single treatment would do the job or if I'd need to bring her back. It worked. Yes it's expensive, but it fixed the problem, and the Methimazole had a cost too. Feb 23, 2018 at 2:22
  • @Monica Wow, it's uncommon for T4 to be that high, but quite a clear diagnosis! Each lab has its own reference range but in an older cat showing signs of possible hyperthyroidism (vomiting, weight loss, etc), I consider anything higher than 2.5 potentially suspicious for hyperthyroidism. The problem is that T4 levels fluctuate over the course of the day, so you never know if you're catching a high point or a low point or somewhere in between. If in the grey zone, I would add on a free T4 and/or cTSH.
    – Harry V.
    Feb 23, 2018 at 4:55
  • I think the T4 was more like 15-20 when the problem was diagnosed and we started Methimazole. Eventually I looked into the radiation treatment and they required a pre-procedure check with the cat off the meds for a week first. That's when it hit 70, but it never got that high while we were treating with drugs. My vet told me she didn't know it went that high and had the lab double-check. Anyway, after the procedure the problem completely went away. Feb 23, 2018 at 15:44

My 20yr old hyperthyroid cat does great with a Twist-a-Dose® from Wedgewood pet pharmacy.
My vet orders the strength of the pens.
My cat gets 2 twists of the pen twice daily applied in the auricle of the ear. No fuss, no bother. He doesn’t mind at all.
So much easier than tablets or other.
They send 2-3month supply at a time — very timely, not expensive. I recommend to all - so much easier than fighting with pills. Ask your vet. He can call it in.
You can order any time of day and night - don’t even have to talk with anyone—it’s all automated with info programmed in.

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