Hyperthyroidism is a common disease that typically affects middle-aged and older cats.  It is caused by an excess production of thyroid hormones, which are produced by the thyroid gland, located inside the cat’s neck. Thyroid hormones affect nearly all organs, which is why thyroid disease can sometimes cause secondary problems such as hypertension, heart and kidney disease.

Causes, Symptoms, and Diagnosis

For a comprehensive overview on what causes hyperthyroidism, what the symptoms are, and how it is diagnosed and treated, read Hyperthyroidism in Cats.

Treatment Options

Currently, there are three treatment options for hyperthyroidism in cats:

  1. Medication
  2. Surgery
  3. Radioactive Iodine (I131) treatment

Surviving Radiocat: A Personal Account

Amber was diagnosed with hyperthyroidism in 2005, and I chose the radioactive iodine treatment for her. For a personal account of our experience, please read Surviving Radiocat.

Can a new prescription diet cure hyperthyroidism?

Hill’s Pet Nutrition claims that its new diet, y/d Thyroid Health, an iodine deficient diet, can cure hyperthyroidism if fed exclusively. My gut feeling, when the diet first came out, was that it sounded too good to be true: simply change your cat’s food, and cure a potentially life-threatening disease? The ingredient list made me cringe. The dry version contains no animal protein; its protein is derived from corn gluten meal, soybean hulls and dried egg product. The canned product is only marginally better: it contains meat by-products, corn and rice. I’m not alone in my misgivings about the diet. Please read Can A New Prescription Food Really Cure Your Cat’s Hyperthyroidism for more information.

Are there alternative treatments for hyperthyroidism?

At a recent meeting of the American Association of Feline Practitioners, Dr. Steve Marsden, one of the chief educators of veterinarians worldwide in complementary veterinary medicine, with board certifications in Chinese herbology, acupuncture, and naturopathic medicine, shared his experience of treating hyperthyroidism with herbal medicine. These medicines may be useful with early cases, as well as during the stabilization phase, and they can easily be integrated into conventional treatment programs. While these herbal formulas are not as powerful as pharmaceutical drugs, they are generally safer and have fewer side effects. At a minimum, they may be able to lower the dose of conventional drugs. Read Herbal Medicine: A New Option for Treating Feline Hyperthyroidism for more information.

Before you make treatment decisions for your hyperthyroid cats, familiarize yourself with all treatment options, and don’t be afraid to ask your veterinarian to clarify anything you don’t understand.

Photo: Flickr Creative Commons

46 Comments on Feline Hyperthyroidism: What You Need to Know

  1. I lived with a cat who had FLUTD and was on one of Hill’s Prescription Diets (both wet and dry). After the Great Pet Food Recall of 2007 I (and many pet owners) started to really pay attention to the ingredients in the foods we were feeding our pets. So I marched down to a local, family-owned store and the store’s owner spent 15 minutes talking with me. The store carried only the highest quality pet food – and by that I mean she required that ALL suppliers had to complete a questionnaire declaring where they got THEIR ingredients. Any company who didn’t comply wasn’t sold in their store. She helped me decipher what I needed to look for, especially in treating Ortoloni’s FLUTD and sent me home with half-dozen or so samples.

    I got him on better quality food (I donated all the remaining Science Diet to a shelter) AND started administering organic OJ twice daily. Because one of his problems was that he was not consuming enough fluids I also started offering him “Mommy Broth”* twice a day as an “appetizer” – after his OJ aperitif and before the main course.

    The transformation was AMAZING!!! He started behaving like a kitten again. I didn’t have a clue that he hadn’t really been feeling well for many, many years. Needless to say, all my cats since then only get the best. I rigorously check ingredients. Spending the extra $$$ is worth it, not only because I want my fur-babies to feel their best but I see it as a preventive measure in warding-off many feline complaints – and vet visits.

    *The pet store kindly gave me this recipe. They showed me before, during, and after pictures of a dog a vet suggested be put to sleep (the poor thing was literally skin and bones), but after supplementing the dog’s diet with this homemade broth it made an astonishing recovery. If anyone would like a copy of it, leave a follow-up comment here.

  2. Hi Nino,
    I’ve been using the Pet Wellbeing Gold for some time now along with Liquid Carn for cats, with my 18 year old cat. I can honestly say that it’s saved her life. I would give it a shot.

  3. Update: My Boo couldn’t take Methimazole. We had to leave her for radiation treatment. ($$) Then she got cancer right afterwards. Then while on chemo pills (and much more for stomach etc) she rebounded for a month or so then got sicker and sicker. I had to have her put to sleep. Lap of Love (Ohio in the US) came to the house. They made sure she was asleep before they gave her the shot to put her down. Wonderful group. Odd thing…when the lady came in the door, Boo hunched down and ran away. She must have sensed what was happening! Poor little girl suffered so much with sickness!!! I kept hoping things would rebound for good…but things got worse. She’d had a feeding tube (when they found cancer they put that in). 24/7 care!!! And she did have some rebound days….I kept hoping it would last but it didn’t. She’d suffered enough. I wouldn’t want to suffer like that so I couldn’t expect her to. I know she’s in heaven and out of pain. I hope she understands why I had to put pills down her throat! I pray she is at peace finally.
    My daughter has a cat though and I will still want to be a part of this group for her sake. She had some mouth problems where the teeth rot out. We had to have most of them pulled so they wouldn’t hurt her when rotting. She throws up sometimes….I’m interested in cooking/at home recepies (sp?) for her cat. She’s about 8 I think. I hate to think what may be ahead for her. My daughter is disabled and losing her Little Girl would be so hard for her. So it’s time to get busy and find out how to do that. I appreciate you all for sharing. Bless you on your journey of cat care.

  4. My 14yo Cat has been diagnosed with hyperthyroid.
    Vet has prescribed Methimazole. Cat has been receiving in ear for past 12 months.
    I have been reading about Pet Wellbeing Thyroid Support Gold – Cat Hyperthyroidism Support. I am considering using this product after reading the “glowing” reviews. However can you advise how this product matches up with Methimazole Please.
    Any advice or experience with both products will be greatly appreciated

    • I would discuss the question of whether The Pet Wellbeing product interacts with Methimazole with your vet, Nino. If the product works as advertised on the Pet Wellbeing website, the methimazole dose may need to be adjusted.

      • Hi Ingrid, Thankyou for your response and that was the first thing that I thought about. My Intention is stop the Methimazole complete and administer Pet Wellbeing Thyroid Support Gold
        I really, Really want information and my question was “Does Pet Wellbeing Thyroid Support Gold work in comparison to Methimazole.
        SAny advice experiences Positive negative feedbacks greatly appreciated

  5. Raw species appropriate diet? My cat has eaten fancy feast (loves it but…) now trying y/d hills but she’s not eating much at all. At 14 with heart trouble and a mass on the speen I’m afraid of radiation or surgery. And the medication….a vet put her into near death by giving her a long acting antibiotic. Most cats die from that (I learned later) but we would drag her out of hiding and hand feed her…putting food and water into a dropper and forcing it down. FINALLY she began recovering (after a couple of weeks). She was so happy she ran around (what she doesn’t do…she’s lazy) and got up on the table! something she hasn’t done in years. But back to the subject…I’m afraid of that Methimazole medication since it’s killed cats as I have read in forums. ANYWAY I said all that to say WHAT NOW? Also forgot to mention, she is a very anxious cat….she is used to certain ways and is spoiled. She shuts down when at the vets….no crying, no trying to run….so with her sensitive nature (scardy-cat) I don’t want her left in the hospital. They said with radiation she’d be there for 4-5 days. That would give her a heart attack. She is so close to us.
    Thanks for listening.

    • Since it sounds like your cat may not be a good candidate for the radioactive iodine or surgery, methimazole is your only option. Every medication comes with risk. Typically, a two-week trial of methimazole will give you a pretty good idea of how your cat will respond to it. The bigger risk to your cat would most likely be leaving hyperthyroidism untreated. I know it’s a difficult decision.

    • Just wanted to say, my cat used felimazole/methimazole for 6-7 years with no problems. You can’t leave it untreated or she will die of it. I wish her well. L carnitine is good to give also and could reduce the amount of methimazole needed.

  6. My cat is 14. She had lost weight but this past week she stopped eating. Took her to the vet & she was diagnosed with hyperthyroidism. I have liquid merthimazole but she still won’t eat & hides from me. What can I do to get her to eat.

    • hi sandy, my cat is also hyperthyroid..what I learned is that the prescription diets are not nutritious and the vets medication is kind of agressive but if a cat can tolerate it, it will at least work to bring t4 down thyroid hormone levels)I chose thyroid herbals and she managed a year on it, lately is not doing good after another vet visit and suddenly has a problem Climbing stairs..she cant take sedation well at her age and its a problem…..that they Always sedate when taking blood…I decided to give her a high proteine natural diet….so mostly meat and as little as posssible go into granes and fruits etc..what hel;ops very well when they wont eat is cooking chicken filet about 10 minutes with a little pumpkin cooked…add nothing….just that and perhaps a bit of olive oil if she or he is constipated…never give dry food since it doesnt contain enough fluid and hurts the kidneys….at the moment I also dont know what to do, since even with medication the tumor or cyst will grow, it cant stop it wich makes me look at her and feel so sad, it can give a problem with vomiting and breathing etc…I cant afford radio iodine, otherwise she would already be at that clinic, it costs 1200 euro in the Netherlands wich is too much for me , considering i am also having health issues and too many bills due to an accident.it really seems to be the best option when they are otherwise healthy.i cant come to giv ing her the vets medication knowing the side effects….and she wouldnt take it anyhow, I tried..i like the herbals, they kept her much more relaxed with less side effects…and i also heared that certain supplementation like giving a cat l carnitine 250 mg a day might help tremendously..I also tried homeopathy wich helps a little…it works great when cats dont have it too severe…good luck with your little friend.give wet food not dry and also watch if she can still go on the litterbox,can pee, because if she cant its dangerous….it might be a kidney stone or blockage……stomache might be irritated from the methimazole>try herbals with l carnitine???

  7. I have a five year old cat with hyperthyrodism. In plain English can someone PLEASE let me know what I sbould be feeding him. Is fresh cooked chicken or lamb ok? Many thanks. Viv

  8. My 11 yr old cat was recently diagnosed with hyperthyroid, we initially brought her to the vet because she was urinating in very large diluted amounts on the bed, it was so diluted I didn’t even realize it was urine, I thought she had thrown up water, she has been drinking alot and is very vocal lately and has lost weight, her numbers were slightly high, so we started her on the low dose meds, do they start working right away and is the large amounts of urine normal? Please help, I’ve been reading as much as possible, but no one has said anything about urination! Thank you!

    • Please contact your vet about the large amounts of urine, Lisa. That’s not normal, and may be an indicator of an additional problem.

      • We just had her at the vet and all her blood work came back perfect, except for the slightly elevated thyroid, thank you so much for responding, any other advice is much appreciated

  9. I have had a lot of experience with feline hyperthyroidism. I had one cat treated with methimazole for years and finally removal of one thyroid. She lived to be 16. Now I have a 13 year old tabby with hyperthyroidism who could not tolerate the meds. My cat received the I-131 treatment. I was more than thrilled with the results. Blood work shows after 12 weeks her levels went to normal. Her weight went up. No more pilling or watching her waste away. It was well worth the $900 we spent for the injection. Now that I have experienced all three ways to treat hyperthyroidism I would choose I-131 without hesitation.

  10. My cat Pushkin is 17+ he was diagnosed with hyperthyroidism and was put on tabs Felimazole this made his neck and head swell so was changed to vidalta 15mg 1 daily, however the longer he had them the thinner he became, until he was just a bag of bones, the vets still insisted he needed them but I had my doubts he was dying right before my eyes although according to his bloods everything was ok. I took him off the meds and he has now gained nearly 1kilo in just 6days and is looking a lot better, he was down to just 3K. I have done a lot of research since and have changed his diet but am having trouble getting hold of something called thyroid support gold which is suppose to help to calm down the over active thyroid and restore a balance, the reports I have read are very positive but it seems that the only place to buy this is on line from America. does anyone know if there is a uk outlet for this, I know Amazon did sell it but they seem to have stopped and don’t know if they will be getting any more, any help with this would be appreciated

    • Charmaine, I found the Thyroid Support Gold thru a site called Pet Well Being which ships International. It’s the one with 472 reviews. Also did you try eBay? I know main stream medicine says this is a case of too much iodine but I started giving my cat nascent iodine and he has settled down so I wonder. I am going to try the stuff from Amazon and this natural herb Carnitine you sprinkle over their food twice a day. Can reverse it in humans and cats and they are too low in it anyway. I just find it odd that here in the USA we are all way way too low in iodine and the Japanese who were much healthier took massive doses compared to our Recommended Dosage by our lovely government which wouldn’t keep a very small rat alive. Selenium is cheap and you and your pets really need that as is a great supplement for warding off cancers. Americans would rise up in horror if they actually had any idea how many of their dogs were dying from cancer. Young ages too.

      • I have a cat with hyper-t and have been trying left, right and center to get this formula – went on to ebay where it said it would ship to Israel – finally, we could start this on her – only to be told by the company via ebay – no, we don’t ship to Israel. But your auction says you do. They told me it was a mistake. So – we are basically without this formula. My cat is 17 and cannot take Methimazole nor do we have any of the options available in the States in terms of treatment. If anyone would like to help us please connect via boisenberryfiesta@yahoo.com

  11. These two websites as well as yours, have been a big help to my cat Ringo. He is 14 and we used the medication route for him when he was diagnosed about 5 years ago. It was toxic for him. He recovered from that illness and we just did the best we could for him, but when I took him in this year, hip numbers were off the chart for thyroid levels. We tried the Y/D prescription diet (canned) for several months with great success. His levels went down to high normal (4) but then he got tired of the food and wouldn’t touch it. I did more research and discovered these two sites and so am making his food myself. He likes the variety I have come up with but the following sites helped guide me. He is due for another blood panel this month, so I will let you know how he is doing. From his behavior and weight gain, I believe it will be within normal limits.
    Here are the sites. One is actually a food list for humans needing to limit their iodine intake.



    • Would you let me know how his bloodwork looked, Terri? I’m intrigued with the possibility of a home-cooked low iodine diet. I’m not familiar with the veterinarian who recommends it on the site you linked to.

      • Ringo is now 16. He refuses to eat the prescription Hills,Y/D diet for hyperthyroid cats. While he was eating it (for about 1/ 1/2 years, he blood work looked normal. Since he refuses the food, we have had to switch. I picked Wellness canned foods for him. He enjoys the variety and doesn’t seem any worse off for now. He also has arthritis and is on prednisone every other day for that. I guess at this point in his life, I am wanting quality of life rather than making him miserable with food he won’t eat or enjoy. I will take him in April to see how his levels are and get a general check up. Looking back, I wish we had done the permanent radiation treatment for him since he has lived for 6 years since the initial diagnosis.

        • Our dear sweet Ringo passed away in April. He had gotten very thin and wasn’t grooming. He didn’t feel well and had no appetite. His thyroid condition was probably the cause, but since he was 16, we felt heroic efforts weren’t necessary. He passed peacefully at home just sleeping away his time. We loved him. Our new kitty who joined us before Ringo died is so much fun and full of life. His name is George. We still miss Ringo but know his time had come.

  12. I would make sure that there are no unknown health issues prior to the radiation treatment. A friend took her cat in for radiation only to have her die due to an previously undiagnosed heart condition. I know it’s a great treament, but like everything, there can be side effects.

  13. Hi,

    I read your post a few months back regarding alternative treatments. My boy is 8 now and was diagnosed last year with hyper -t. Since only his free t4 was high and he is so young I decided to try the alternative route. I’m happy to report that we caught the disease early and it is in check. Here is what worked for us:

    1) Switch to commercial raw food (we use Primal or Natures’ variety – mostly Primal)
    2) Used Thyroid Support Gold from PetWellbeing – we were on 5 drops 2x per day but now
    reduced to 3 drops 2x per day
    3) Used 250 mg l-carnitine split in 2 doses each day (we have discontinued this since his
    values are normal)
    4) 30 mg of coq10 1x per day
    5) probiotics and digestive enzymes
    6) Ultra EFA from RX Vitamins for pets we use 1/8 tsp mixed in food 2x per day

    I am not a vet and have no medical training but I am happy to share that this worked for us – most likely because we caught the disease in an early stage.

    I have used I131 in the past with another older kitty – she was 18 and it made a big difference in her overall health although she developed cancer and we lost her about 6 months later.

    Best of luck to anyone who is struggling with this disease!

  14. I also have a hyperthyroid kitty. My kitty gets the gel pen in the ears. My vet told me to wear gloves. And I wash my hands. We were on pills before. My kitty will be 21 this July and I am one of the lucky ones that he can tolerate meds. They only had surgery when he was first diagnosed and it was only a 50% chance. And pricey. Now they have so much more and also know so much more than when we found out. He just got high blood pressure this year so the vet is keeping a closer eye on him. He is doing pretty well.

  15. As someone that was hyperthyroid for 8 years, I was faced with some of these options as well. I am pleased to hear that RAI works so well in cats. I am concerned about how vets handle the exposure to human pet owners and other pets in the household to these solutions.

    I recently found out that there is a Methimazole gel you can rub on their ears – however, the reader that told me this wasn’t aware of the dangers of her hands being exposed to that Methimazole gel. It appalled me that the vet didn’t convey to her that it could affect her!

    • Cats have to stay at the I131 facility for 3-10 days (regulated by the state), Jenny. The residual radiation these cats have is minimal, and you probably get worse exposure from standing near your microwave or watching tv! The transdermal methimazole should have come with instructions to use a glove when applying. In fact, this is true for most transdermal meds – it stands to reason that if they’re absorbed by the cat’s skin, they will also be absorbed by human skin.

      • Lisa here: I second what Ingrid said about I131. It only has a half-life of 8 days, so the levels quickly diminish. I like the “precision targeting” approach of I131 – especially after hearing the AAHA’s report in March on recent findings: new studies now indicate that sarcomas (cancer) are responsible for up to 25% of all hyperthyroidism in cats, as opposed to the 2-3% that had previously been thought.

        Also I like the stats on I131 – and surgery too: cat guardians who choose these options over Methimazole have longer survival rates.

  16. Hi Ingrid, just saw this post on your Google+ feed. Nice work. It quickly caught my eye as I just recently contributed to an article about thyroid disease (in both cats and dogs) for The Oregonian newspaper – it ran this past weekend (http://www.oregonlive.com/pets/index.ssf/2013/05/pet_talk_thyroid_disease_a_man.html).

    Always love reading your stuff. Hope you had a great time at BlogPaws. I was sad to not have made it this year, but am hoping to do so again next year.

    Be well and have a great day!


  17. As I think I wrote on another post related to this, our Jackie kitty was diagnosed with hyperthyroidism several years back. We tried the medical approach but her case was too severe so we decided to go with the radioactive iodine option. It was a complete success and she has been fine, we just took her in for a checkup last week and are having a thyroid panel done to be sure everything is still ok.

    So keep her in your thoughts or whatever you do, will let you all know how her results come out.

    Tom Mary Beth and the furries.

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