Hyperthyroidism, the overproduction of thyroid hormone, is relatively common in aging cats and may explain changes in behavior, weight loss, vomiting and diarrhea, among other signs, writes veterinarian Andrew Riebe. Findings from a physical exam including a heart murmur and palpably enlarged thyroid gland along with a blood test measuring hormone levels provide veterinarians with a diagnosis. Dr. Riebe explains the advantages and drawbacks of available treatment protocols for feline hyperthyroidism, including a new food that alleviates the condition if fed exclusively. WANE-TV (Fort Wayne, Ind.)


Clinical Signs:

There are various clinical signs or “symptoms” that a cat with hyperthyroidism may display.  Some of the most common signs include weight loss, changes in appetite, gastrointestinal disturbances (e.g., vomiting and/or diarrhea), and changes in urination.  Affected cats may also show changes in activity level and attitude.  If you ever notice any of these signs in your cat, schedule an appointment with your veterinarian immediately.  These clinical signs are caused by the over-production of thyroid hormone by the cat’s thyroid glands, which are small endocrine glands located on the cat’s ventral neck, just adjacent to the windpipe (trachea).


In many cases, a veterinarian will become suspicious of hyperthyroidism based on a history of common clinical signs and findings from a complete physical examination.  Some of the most common findings on physical examination include evidence of weight loss, dehydration, and the presence of a heart murmur.  In some cases, the veterinarian will be able to feel a lump or enlargement on the thyroid gland itself.  To confirm a diagnosis of feline hyperthyroidism, blood tests are used to measure the levels of thyroid hormone circulating in the cat’s blood, which will be elevated in affected cats.  Remember that all cats need to have a veterinary examination performed at least once each year so that diseases like hyperthyroidism can be identified as early as possible.


There are a few different treatment options available for cats with hyperthyroidism, all of which have their advantages and disadvantages.  Traditionally, the most common method for controlling hyperthyroidism is the administration of anti-thyroid medications that help to suppress the production of excessive thyroid hormone.  These medications are often effective and are relatively inexpensive, however life-long treatment is required and some cats will develop significant side effects.  A more definitive treatment option is also available, which involves the administration of a radioactive iodine injection to the cat. The radioactive iodine is only absorbed by the overactive thyroid tissue, which results in the destruction of this abnormal tissue.  This procedure is very safe and typically very effective, however it is associated with higher initial costs and requires the cat to be hospitalized in a specialized facility for several days.  More recently, a new therapeutic diet was developed for cats with hyperthyroidism.  The therapeutic food has restricted levels of iodine, which is an essential component for thyroid hormone production.  Therefore, by limiting the cat’s intake of iodine you are also able to limit the amount of thyroid hormone that the cat can produce.  This option offers the ease of providing treatment by simply feeding the cat, however, the cat’s diet must be strictly limited to the prescription food, which can sometimes present a challenge in multi-cat households or in cats with picky appetites.  Finally, surgical removal of the thyroid gland itself is also a method for treating hyperthyroid cats.

No matter which treatment option is selected, many hyperthyroid cats can be effectively managed and will often show improvement, if not resolution, of their clinical disease.  Nevertheless, long-term monitoring and regular veterinary checks are important for affected cats.  If you have any questions about this disease or if you think your cat may be showing signs consistent with hyperthyroidism, contact your veterinarian immediately.



46 responses to “Feline hyperthyroidism: Symptoms, diagnosis and treatment”

  1. Thomas Regler says:

    Has anyone used Hill’s Perscription Y/D? I am having trouble getting my cat to eat either the dry or wet. Was wondering if you can put, say, tuna water from canned tuna in it?

    • That is a quick call to the vet. The prescription diets are finely tuned for specific ailments and any alteration can throw the animal “off” and impead their progress, so I would take any chances.

      • karen says:

        its been a few weeks now since starting the Y/D diet
        She has totally rejected the dry food…vomited every day…..she eats the canned food but is still vomiting about every three days.
        will this stop?…we are very concerned about her weight.otherwise she runs and plays and seems happy.
        she is 13 years old…..had been on average 16 lbs…is now 11lbs.

    • GN says:

      Aside, from the lack of iodine, the Y/D diet is nutritionally deficient and will make your cat unhealthy in other ways. My elderly kitty was on it for a few months and had constant vomiting and diarrhea from it — he was miserable. The vet insisted that I persist, but I refused. I put my boy back on a Wellness diet and resumed his Tapazole medication. I would not recommend the Hill’s diet.

      • ymie Thiulle says:

        I agree that I also, would not recommend Hill’s diet. I have an older cat (14) and when she had vomiting and diarrhea problems they recommended Hill’s Science Diet. It was expensive, she hated it and would barely eat, lost more weight and had the same problems. Eventually, I switched her to a cooked ground turkey with added Omega 3 oils and a very small amount of spirulina with great success-no more vomiting, no more diarrhea, she gained some weight back.

    • nicole says:

      its really not a good idea to put our tuna in there food because its really not good for them however you can try and put a little wet, I suggest wellness simple because it has limited ingredients which should be ok, just check with your vet. a lot of cats don’t like any prescription foods so it can be a little difficult. if your vet says no you can also try royal canin low calorie. these should help, just use about a table spoon.

      • Sue says:

        Why isn’t tuna good for cats?

        • Robert Pavlick says:

          Tuna, as well as all fish contain some mercury, so fish should not be given for every meal.

          But in the case of human packed tuna, heavy metals accumulate in the liver, thyroid, pancreas and kidneys, and destroy the digestive system, causing issues that a owner may not see symptoms from for awhile.

          Human grade tuna is packed in salt water and the tuna is salted, so it’s bad for cats, the salt is hard on their kidneys and can cause major problems if fed often. It also is missing Taurine, a necessary element for good health in cats.

          1.Taurine deficiency in the cat results in Feline Central Retinal Degeneration (FCRD). When taurine is deficient, the photoreceptor cell membranes
          become disrupted and dysfunctional, which eventually leads to cellular death and the loss of cells. Complete blindness ensues with full degeneration of the retina and attenuation of retinal vessels. Structural changes within the retina are permanent.

          2. Taurine deficiency in the cat also results in the development of dilated cardiomyopathy (DCM). This degenerative disease causes decreased myocardial contractility, which eventually leads to cardiac

          3. Taurine deficiency adversely affects the cat’s immune response against infectious organisms (viruses, bacteria, parasites) and malignant and metastatic disease.

          See: http://maxshouse.com/Tuna_and_Cats_Nutritional_Facts.htm for a full list of problems with tuna packed for humans.

          Please don’t be stubborn by continuing to feed your pet anything toxic, just because there are no immediate symptoms. You are shortening your pet’s life.

          • Catguy says:

            In addition, canned tuna may have iodine. Salt is commonly processed with it. Iodine is what the Hills product is designed to avoid. It is a low iodine formulation. Chances are high the tuna water would defeat the purpose of the food.

    • Sarah says:

      When our cat was diagnosed with hyperthyroidism, the vet’s first advice was to take tuna out of her diet. She said that the tuna is high in iodine. Since the hyperthyroidism is aggravated by iodine, I would suggest you not use tuna or tuna water. We have tried the Y/D dry which my cat ate well during the first three days, then she seemed to tire of it. I haven’t been able to try the wet because that’s still on order.

    • Margit says:

      Most important remember they are carnivores, period. Their systems aren’t made to eat grain and a lot of other high carb items, such as sweet potato etc. I only feed my cats grain free wet food, such as wild callings, instinct, evangers, wellness.You can get most of these on amazon or petvalu has a lot of grain free for cats. I have 2 siamese they are 14+ and look like they are 4 instead. I never fed them grain and often raw like bravo. You can google raw and how to make the change over slowly if this is what you decide. I can’t believe vets still recommend grain for cats.

  2. Bryan says:

    Here is another good article about feline hyperthyroidism.


  3. Jayne says:

    Sorry your cat is throwing up. Best to stop feeding the Y/D. Do some intense research online on the best foods for her. Please find another food that she will eat without throwing up, Vets receive very little training on cat food, therefore, you can’t always depend on their input regarding cat food. Good idea to stay away from canned fish and use chicken or turkey canned food.

  4. Lisa B says:

    My one cat did fine just taking her Methimazole. I had another cat who started losing weight but there was no diarrhea. I waited too long,thinking it was nothing too serious. My doctor said his thyroid count was high so he was also put on Methimazole. He barely started his medication and I called to say something was definitely wrong! I brought him in and all they did was give him fluids w/ vitamins and had me purchase some stomach medication, thinking his meds were making him not feel well. The vet closed early and an hour after I brought him home he started dying. I had no one to help . He died on my couch that evening. It was horrible and I blame myself for not bringing him in sooner and the vet for having a tech give him fluids when I had called the vet earlier and told him something was really wrong with him. I still cannot stop grieving. Cats aren’t always good at letting us know when something is truly wrong. Take them in immediately if you notice ANY changes. It may save their lives.

    • Julinka says:

      Maybe something else failed besides his thyroid. I don’t think you should blame yourself too much.

      I waited a bit after my 17 year old kitty started losing weight thinking it was just old age. When she had a blood test, the vet told me it was hyperthyroidism. Started her on the pills, but she reacted too strongly to the meds. Threw up continually, so she is off meds for now and doing OK while I figure out what to do next. I hate to say it, but maybe it was just your cat’s time to go. You sound like a good cat mom. We always feel we can change the outcome “if only” but sometimes we can’t.

  5. kathryn says:

    My cat is 16 years old and has hyperthyroidism. We have the choice to have him treated (which my vet says will be expensive and could be deadly itself because of his age). He has horrible diarriah and throws up all over the house. We’re thinking about authenizing him. What would you do?

  6. Julie B says:

    My cat is 16 and has every clinical manifestation of hyperthyroidism, including the heart murmur. When his blood tests are sent in they always come back with no indication of the level that would confirm that he has it. So the vet won’t give us the meds he needs. I asked her if we could try him on a low level dose to determine if it would help him. The answer is ,”No.” Would a low dose be extremely dangerous? We are at a crossroads. We either try something or just let the numbers dictate his death. Does anyone know why this happens? Anything we can do about it? He’s been attached to me for 16 years and I to him. He’s my very best buddy. Could a different lab make a different outcome?

    • Catguy says:

      Get a second opinion and examine the blood work results closely. For what it is worth, my cat has the exact same condition and has had it for quite a few years. Still around at 19, untreated. Decided to finally try the Hills, but doubt I’ll be getting more once the bag is gone. Cat doesn’t like it. May consider meds at that point, maybe not. When they’re this old the blood work and stress of going to the vet for it isn’t good for them either. Quality of life is important. Unfortunately our beloved pets don’t live forever.

    • Dee says:

      get another opinion

  7. Dee Wynn says:

    I had a cat who had hyperthyroidism and lost weight to less than 4 lbs. This morning she was lying on the coffee table and crying. I picked her up and her little body started jerking and she was crying. Please tell me what was going on with her at that time. All I could do was to hold her close to me and tell her that I loved her. My vet wouldn’t be open for another hour. Please tell me she wasn’t hurting. She was over 18 years old.

    • Raymond Charron says:

      My cat was crying at times too. I forgot to put that in my post. It was a nor rowing cry. I brought him to a vet and a blood test told him everything. He had feline hypothyroidism. Read my post. I hope you did that as I did. Cats are family. When they hurt you hurt. I hope you did what I did. Now he’s doing just fine, thanks yo the medical procedures that were fine.

  8. Jenny says:

    Hello, we have a beautiful 9 year old pixie Bob named Ruppy that was just diagnosed with hyperthyroidism yesterday. I am devastated. While naturally he is a big boy of a normal 18 pounds he is sinking fast…now less then 14 pounds. We have several options. One of them being radioactive treatment one time that kills the over active part of the thyroid only. The other options are basically what I’ve read here. The hills y/d food would NOT make me feel at ease to treat his condition. Since this is endocrinology (hormones) I believe this is and can be life threaten in an instant. Depending on how much of his thyroid is involved and such I would also consider surgery. There are plenty of medications to give him, however, all the information I have read is that while it gets control over the active secretions, it is not considered a long term treatment….additionally can take awhile to get the correct mgs to get it subdued. During this time, my poor fella is wasting away. I want a more permante solution if there is one. Ruppy is otherwise healthy. He is the alpha male of the family and a young senior kitty. Anyone out there have any experience with radioactive therapy?

    • Diddy says:

      I just took my Bobbie for the radioactive iodine treatment. I’ll try to remember to let you know how it goes. I’m scared to death for him, but was willing to try this as opposed to him being cut upon and put to sleep at 11. His first night away from home and I’m devastated. Aren’t I the typical mama?

      • Yes, you’re a loving and caring mama!

      • Bikermo says:

        MY 16 year old, Tiger, who’d been with me through everything, suddenly had trouble breathing so i took him to the vet to get it checked. that night i took home an empty carrier and a week later i picked up his ashes. then my 13 year old, Toby, started meowing all the time out of the blue and was very antsy, i attributed it to missing his big brother, who had been there from the moment i’d brought him home. But last weekend he chewed on a white sock and left blood behind, so i took him to the vet for blood work before getting his teeth cleaned. he was diagnosed just last night with hyperthyroidism, and i was given the same three treatments: diet, meds, radiation. PLEASE let us know how your Bobbie tolerates the treatment, and about his recovery afterward. I told my own mother this morning, for someone who never gave birth i sure feel like a mother today!

        the worst is that my Dad was killed in a crash in august, so for six weeks i was barely home with my boys for more than an hour a day, and now one is gone and the other is very sick. can’t help but wonder if i’d have caught on sooner if i’d have been able to be home with them. been a crappy six months!!

        • Juls says:

          I’m sorry for your losses! I went through a similar experience several years ago. My mother was very ill in the hospital, during which time one of my cats was becoming ill but I did not pick up on it because I was spending so much time at the hospital. My mother passed away. and then I found out that my cat had age related kidney failure, and she died shortly after. A few weeks after that my other cat stopped eating,and, in my opinoin, died of a broken heart, as my two cats had spent thier whole lives together. He too, was very old though. It was a very difficult few months. Since my beloved kitty was elderly it wouldn’t have made much of a difference if I had known sooner as far as the outcome, she was just near the end of her life. Maybe it’s the same with your kitty. Although I would’ve like to have spent more time with her, I needed to be with my mother. I focused on all the years before that that we had together and that helped me while grieving. My cats were 18 and 19.

      • Jennifer says:

        How did your cat do with the iodine treatment?

  9. Jerry says:

    When I mentioned to my vet that my 13 year old manx, always a crazy little monster, was acting like she was a kitten, he diagnosed her hyperthyroidism. We put her and our other cat on the Hills Y/D and had great results, we just slipped some regular wet food to the other cat to get her the iodine she needed. While the Y/D was expensive, it worked well and she tolerated it with no problem. Giving that little psycho a pill twice a day would have been interesting to say the least. She passed away at 17 from other issues last November and I still miss her so much. Since then, the other cat has developed the same hyperthyroid but she is much more tolerant of the meds, I just put the pill on top of a spoonful of Trader Joes “Tuna For Cats” and she wolfs it down about 80% of the time, if not, she isn’t that difficult to pill.

  10. Raymond Charron says:

    My older cat was experiencing diffulculty in breathing. Coughing and sneezing. The sounds were horrible. Besides all that, he just didn’t look well. He wasn’t active like he had been, so knew something was wrong. Took him to a vet and he performed a blood test among other minor things. The test results showed he had feline hyperthyroidism. Surgery was suggested. The vet did a thyroidectomy among minor things that go with that. It was in and out. Got him home and he’s doing fine. He eats well, drinks well and does a lot of sleeping. Heck, I would too if I had that kind of surgery. It was a challenge to administer the meds prescribed by the vet, but succeeded. He’s doing fine now and I hope he stays around for many years now.

  11. CaraT says:

    Our 10 year cat was just diagnosed with hyperthyroidism. She has lost about 6 oz. in weight over 2 years. She is one of 3 cats here and our vet suggested that we start out by trying the prescription cat food that does not contain iodine.
    I have a lot of experience with thyroid issues in humans (me) and I am sure that the vet was surprised by my many questions based on my experience over 30 years of thyroid issues.
    What I forgot to ask was…how will having an iodine free diet impact our other two cats? Are there foods I should sneak to the other two cats to get them some iodine in their diet?

  12. sue mcnelly says:

    First what is YD that many comments refer to??? My 11 year old Lili was just diagnosed with hyperthyroidism three days ago. Second: it would be very helpful when people offer remedies to offer amounts. Such as how much Omega 3 oil to ground turkey and what is a small amount of spirulina (??) to turkey?? Too many people have commented negativly about Hill brand so I won’t be trying that. I was hoping to learn of an over the counter food I can try before committing to the process of radioactive treatment. Unfortunatly I am leaving town in six days which does not leave much time to transition/try a new food and time is ticking away waiting for the vet to call back. Hence my going on line. With 5 days of special high energy can food and Proviable DC her diarrhea (only sympton) has cleared, she is returned to eating her Royal Canin senior brand and back to herself. I guess I am to the point that prayers will keep her well until I return i about a week

    • It’s a prescription diet for cats with thyriod issues (Hills). We are not prescribing this – we do not do that. You should ask your veterinarian for any information concerning changing the diet of a pet with thyroid issues.

  13. Judy Strandlien says:

    My cats hate Hills Science Diet itself, I can get them to eat it if I mix a little Fancy feast in with it. I have one cat with hyperthyroidism and another with seizures. My cats love “cat concoctions”. The one with hyperthyroidism has all the symptoms, weight loss (1pound), hyperactivity, crying more but hungry all the time. She is on meds so I hope her thyroid level goes down.I feed them what they like and pray for the best.

  14. Weed Lover says:

    After I originally commented I seem to have clicked the -Notify
    me when new comments are added- checkbox and now each time a
    comment is added I receive 4 emails with the same
    comment. There has to be a way you can remove me from that service?


  15. Rosie Rogers says:

    Our cats are 13. Pumpkin was just diagnosed with hyperthyroidism not just 1 gland but both. We’re going to do the radioactive treatment. A 1 and done deal. No pills and no crappie science diet shit. I worked for a company that sold science diet and everyone that bought it brought back the unused food saying their cat REFUSED to eat it. I can’t wait til my Pumpkin is back to his normal self.

  16. Gayle Wocoski says:

    My beloved Teegan was diagnosed with hypothyroidism 3 years ago at the age of 9 years old. We decided to put him on .02cc of Methamazole 2X a day. He was fine on that dosage for 3 years and in May 2017 at his required 6 month blood work check, his thyroid counts had almost tripled. Our vet said this can be a normal occurrence as a cat with hypothyroidism ages. They now have him on .04cc of Methamazole 2X a day and he’ll be going back in about two weeks for bloodwork,to see if the new higher dose of Methamazole is doing the job.
    My hubby and I pondered over the three different treatment plans and decided that the Methamazole route was the best for Teegan. He’s a rescue cat we got when he was 18 months old and he had never lived in a permanent home before ours – it was either at the Humane Society or in foster homes. He had a cancerous lesion removed right below his left eye 5 years ago and didn’t take well to be left for a short time at a specialist’s facility. He is terrified to go in the car, visit the vet for ANY type of visit and is paranoid and hides when anyone knocks on the front door or rings the bell. I know he would never survive the radioactive iodine treatment with being at a estranged facility for a week, and then no real interaction with my hubby and I.So we are praying that the Methamazole continues to work, even if we have to increase the dosage again. Teegan was within about one week of being euthanized when I saw him on the Humane Society’s website and fell immediately in love with him! Our previous cat had died two month’s prior to me finding Teegan. We give our cats the best food and treats (both dry and went food is grain free, etc), we take them to the vet at the first sign of anything unusual as he is a member of our family. I can only say in closing, that our experience so far with hypothyroidism has not been horrible, I feel that we chose the right treatment for my love muffin and we will change course when and if we feel our current treatment plan is not working. I wish you all the best in your choice of treatment for your beloved kitties!!

  17. Ms. Dale Gibson says:

    I am taking care of my friends beloved “Blurt” (that’s his knickname). He does have the thyroid thing and I give him the Methamazole twice a day. I called her today to say he was not eating as well and not drinking as much water than other times I had him. I am owned by a cat, too, but he is younger and stronger than Blurt. I have seen from these messages that increasing the M thing is good. I’ll try that tonight and if he doesn’t improve, they will have to come home from Pennsylvania. I appreciate you people sharing your stories about being owned by a cat and the tortures they put us through. I find it very hard to discuss being an owned human – some people just don’t get it. Thank you for your good wishes – they made me optomistic. P.S. His name is Tchykofsky (sp?) You know the concert pianist from long ago? As in “dance of the sugar plum fairies” Walt Disney’s Fantasia. Blurt is much easier.:)

  18. Mary says:

    I had a cat Stripee who had hyperthyroidism when he was 11. He lost over six pounds in a short period of time. I knew something was definetly wrong. I opted for radiation iodine treatment and worked great. Is expensive, but works. I recently had another kitty Piggy that had it around the age of 9. Tried the medicine with her, but had to keep paying for blood work to alter the meds as needed. Her name is because she eats anything, but that special Hills diet made her sick all the time. Ended with surgery and radiation since it was progressing quickly. Two years now and she’s doing great. She had to be sedated any time they needed blood

  19. Sally Morton says:

    My 13-year old spayed female cat has three times the maximum accepted level of thyroid, yet is obese and inactive. So which is correct, the test or the symptoms?

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