PetMeds® Treating Hyperthyroidism in Cats

Hyperthyroidism or an overactive thyroid is the most common hormonal disease seen in older cats. The most common symptoms include weight loss (despite an increased appetite), as well as increased thirst and urination. Some cats may become more restless and vocalize more, as well as develop inappropriate urination or defecation. If left untreated, hyperthyroidism can lead to high blood pressure, kidney damage or secondary heart disease.

Diagnosis is usually made by blood measurement of Thyroid levels, usually a T4 in conjunction with a free T4. There have been traditionally three options of treatment. The most common form of treatment is with a prescription medicine known as Methimazole.  This medicine must be given daily to twice daily, and periodic thyroid level  blood monitoring is needed every 3-6 months after initial control is obtained, , as well as monitoring of the blood count, and liver/kidney function  to make sure there are no ill effects of the medication.

Occasionally cats will become lethargic, vomit, or lose their appetite on Methimazole. However, with dose adjustments, most cats do tolerate Methimazole quite well, which needs to be maintained for the life of the cat. Other options of treatment include using radioactive iodine, which is preferred by many as a single dose curative treatment in most cases.  Surgical removal of the thyroid gland is no longer as common, due to surgical risk in many of these older cats.

In my experience there are not that many effective supplements for cats to treat the overactive thyroid, however, if your cat will accept cooked brassica veggies like broccoli or kale, these can sometimes have a thyroid-lowering effect. The herb bugleweed has been used by some, but data as to efficacy is limited.

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  1. Oops, I do have one more question. I have two other healthy cats. Is there any danger to them in using the same litter box as my kitty who’s receiving the felimazole? Thank you!

  2. Is 7.9 T4 level critical or just considered HIGH, from 5.9 being the normal ?

  3. Dr. Michael Dym, VMD veterinarianMay 27, 2014 at 9:23 am

    7.9 is high but is not critically high in most cases, however each case must be assessed individually.

  4. Dr. Michael Dym, VMD veterinarianMay 27, 2014 at 9:28 am

    No danger at all

  5. Dr. Michael Dym, VMD veterinarianMay 27, 2014 at 9:30 am

    Usually thyroid levels return to normal within a few weeks of starting correct dose. You should have levels rechecked. Not sure about the cleaning of ears. Consider asking 1800petmeds pharmacist. As for preventing future blood clots, I would also ask your vet about having an echocardiogram to rule out concomitant cardiomyopathy in your cat which may need its own medications as well.

  6. Thank you, Dr. Dym!

  7. Hi doc. I’m checking in after almost a year. My kitty is now 18 but still looks years younger. She has some arhtritis in but you wouldn’t know it unless you saw her jump. She goes to town on her upright scratcher a few times a day so I know she doesn’t have any serious pain. She’s a happy cat.who makes cooing noises upon eye contact and is a monstrous purrer.

    She’s been on the y/d for over one year because the radiologists (the ones who offer I-131) refuse to take a \risky\ patient and so denied us the I-131 treatment. I think she would have benefited, but she’s doing well on the y/d. in additon to y/d, she receives 50ml LRS sq nightly and Vetri-Science renal essentials chews. I add Rx-Zyme and Amino B-plex liquid vitamins to the y/d which I feed 3x day. She is still naturally flea-free and has a beautiful, clean, shiny white coat and bright eyes. I am happy with the y/d though I didn’t expect her to thrive on it.

    I have a suspicion that y/d is not so much a low iodine food but instead relies on it’s L-cysteine content to remove iodine from the pet’s body. What are your thoughts on that?

    Wanted your opinion on methimazole \tricks\ in case I do resort to trying that again. If a cat doesn’t tolerate methimazole (nausea, even when applied to pinna) but eventually needs more than the y/d, would you condone daily maropitant in order to increase tolerance of the methimazole?

  8. Dr. Michael Dym, VMD veterinarianJune 2, 2014 at 6:19 pm

    HI Nik. Actually not sure exactly how Y/D diet works so I would check with Hills company who makes it. Also as for methimazole, it certainly can help many cats, but if side effects intolerable, other options like surgery or iodine are needed. I dont have experience using maropitant(cerenia) in cats who can’t tolerate the drug, but certainly worth a try.

  9. Starky has been on the compounded methimazole(liquid form) for 2 years now without any side effects. I would recommend this since Starky has been able to tolerate it and it has not even effected his kidney, lungs or heart. He is doing great and he is almost 22.

  10. Thanks doc. Sorry my middle of the night post was so rambly. You did a thorough job of answering my questions, and I appreciate it.

  11. Dr. Michael Dym, VMD veterinarianJune 3, 2014 at 3:36 pm

    You are very welcome

  12. Dr. Michael Dym, VMD veterinarianJune 3, 2014 at 3:43 pm

    Thanks Sandra for sharing this with us

  13. You are very welcome 🙂

  14. I’m wondering how long it takes Plavix to start working in a cat. The emergency vet put him on it about three days ago following what they think is a blood clot that caused him to have one of his hind legs go out on him for about a half a second. He had a similar incident several weeks ago, which took us to the regular vet’s and they discovered he had hyperthyroidism at that time. He’s been on felimazole for almost three weeks. The emergency vet took x-rays last weekend and sees a thickening in the heart, and my regular vet is scheduling an echocardiogram soon. So I was just wondering if the Plavix is already working for him, and if it’s likely to help prevent a future blood clot. Thank you..

  15. Dr. Michael Dym, VMD veterinarianJune 13, 2014 at 7:00 pm

    Plavix will usually work quickly No definitive data on its efficacy but theoretically may lessen likelihood of future clots

  16. Thank you, Dr. Dym! My hyperthyroid kitty did have his echocardiogram and the cardiologist said his heart funtion was normal and there were no “findings that suggest a cardiovascular cause for the episodes (two brief episodes of hind leg collapse) either thromboembolic or otherwise.” The report stated that no cardiac medications are advised. So my vet took him off Plavix. His first blood test since he’s been on methimazole was just done and shows that his thyroid level is now normal and he’s starting to gain weight and seems like his old self. So I’m curious as to what might have caused those previous episodes, where his hind legs collapsed for one to two seconds (this was before he was diagnosed with hyperthyroidism). Do you any thoughts on what might have caused this? Could it have been related to untreated hyperhyroidism? Thank you…

  17. Dr. Michael Dym, VMD veterinarianJune 15, 2014 at 9:52 am

    Glad to hear he is doing well. Hyperthyroidism when not treated, can lead to hypertension and possibly mini strokes which sounds like that is what my have occurred. Now that hyperthyroidism under control and likely no more high blood pressure, hopefully he will be ok.

  18. Thank you, Dr. Dym! ^..^

  19. My Lola is a 17 y/o female feline…diagnosed w/hyperthyroidism…my vet prescribed the Felimazole 2.5 mg twice a day…got her the Methimazole 5mg…quite the bargain…I use a pill splitter (thank you to my Walmart Pharmacist)…into her Fancy Feast it goes as she will now not eat anything else. Happy to report it’s been quite the emotional 2 month journey…as of today she is doing great!!! A big thanks to PetMeds for all you do for us animal lovers.!

  20. I have a 13 yr old cat, Jessie, who was diagnosed with hyperthyroidism about a month ago. After several different doses of the oral medication, Jessie stopped eating and vomited several times a day. He is now on a strict diet of y/d canned food, which he liked for a couple of weeks, and then stopped eating. He consumes only a couple of tablespoons a day. I’ve mixed it with some canned tuna, but he is still turning his nose up at it. I considered ordering Thyroid Support Gold, but now am not so sure after reading the reviews here. My next choice is the ear medicine, but am very concerned that my cat is eating so very little and is continuing to lose weight. I would appreciate any suggestions.

  21. My cat has been taking the liquid methamizole for a little over 2 years now and is doing fine. I let him eat whatever he wants. That is the methamizole compounded. He has had no adverse effects whatsoever. Before this I tried the y/d and he did not like the wet food at all. To make him gain weight I am giving him the Science Diet kitten food. He will be 21 next month.

  22. Dr. Michael Dym, VMD veterinarianJuly 15, 2014 at 3:57 pm

    I think the kitten food is fine, as it has alot of protein…. especially if his kidneys are ok and he not like Y D food

  23. Dr. Michael Dym, VMD veterinarianJuly 15, 2014 at 3:59 pm

    I would consider the radioactive iodine therapy, however make sure your cat has had a full medical workup to make sure no other medical issues involved with loss of appetite

  24. A friend of ours tried the iodine therapy and her cat got so sick they had to put him to sleep and he was only 10 years old. She really regrets ever having done this. She was so upset.

  25. Dr. Michael Dym, VMD veterinarianJuly 15, 2014 at 4:13 pm

    Thanks for your compliments

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