Last Updated on: April 29, 2013 by Ingrid King


For the past few months, the veterinary community has been bombarded with ads for a new feline prescription food that is said to cure hyperthyroidism in 3 weeks.

When the diet first came out, I was skeptical. I’m not a fan of prescription diets. While I respect the research that goes into these diets, sadly, they usually contain ingredients such as meat by-products, corn, soy and grains, none of which are optimal for an obligate carnivore like the cat.

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.

There are currently three treatment options:  lifelong medication, surgery, and the gold standard, radioactive iodine therapy. A single injection of Radioiodine (I-131) cures 98-99% of feline hyperthyroidism cases without any adverse side effects. There aren’t many diseases that have that simple a cure and such a high cure rate.

Hill’s Pet Nutrition’s new diet, y/d Thyroid Health, is supposed to provide a fourth option for pet owners. My gut feeling 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.


Having dealt with a hyperthyroid cat, and understanding the challenges of either giving twice daily medication for the rest of the cat’s life, or facing the considerable expense of the radioactive iodine treatment, I would love it if a cure could be a simple as changing a cat’s diet. However, after doing some research, I’m not convinced that it’s a simple as that, even if a cat guardian would be willing to compromise on good nutrition and feed a diet with what I consider questionable ingredients.

Dr. Jean Hofve, a retired holistic veterinarian, wrote in her Little Big Cat newsletter:

“While Hill’s admits that there is no scientific evidence that excess iodine causes hyperthyroidism in cats (in fact, their staff veterinarian stated that if iodine were actually the problem, every cat would be hyperthyroid!), they nevertheless claim that this diet, fed exclusively, will normalize a cat’s thyroid levels in 3 weeks. The diet has been tested for nutritional adequacy by feeding trial in approximately 14 cats; some cats ate the food for 1-2 years.

Time will tell if y/d will be a “cure-all” for feline hyperthyroidism; and if it’s truly safe for long-term use. The claims being made by Hill’s seem pretty outrageous for a generally conservative company. Expect these claims to be vigorously disputed by many.”

Dr. Eric Barchas, veterinary contributor to Catster, remains skeptical as well. In his article Can a New Thyroid Health Food Live Up to the Hype?, Barchas states:

“So far, I have tracked down only two studies on y/d. Both consisted of small samples run over relatively short time periods, and both were run by Hill’s. Both showed that the diet is effective, but anyone with a shred of scientific background should be able to tell that the studies aren’t very strong, and that more research is indicated.

Larger, long-term studies are needed to determine what happens when cats without thyroid disease eat y/d. Plenty of people have more than one cat, and cats eat from one another’s bowls. Also, a very significant number of cats with hyperthyroidism also have kidney disease. How will this diet affect kidney function? Finally, most people like to plan on their cats living for several more years (I would hope that a 7-year-old cat diagnosed with hyperthyroidism might make it to 15 or even 20). I believe the longest study on record so far lasted two years. What will happen to cats that eat y/d for 10 years?

In short, I believe that Hill’s has unleashed y/d with too little research and too much hype.”

Amber became hyperthyroid in 2006, and I chose the radioactive iodine treatment for her. If I were faced with a diagnosis of hyperthyroidism for one of my cats again, I would most likely make that same choice again. I definitely would not choose this diet.

Photo by Bruno Cordioli, Flickr Creative Commons

35 Comments on Can a New Prescription Food Really Cure Your Cat’s Hyperthyroidism?

  1. My 14 yo cat was diagnosed with hypothyroidism 3 weeks ago, he was put on a k/d diet to protect his kidneys. The first couple weeks he would eat the dry k/d food now he does not want to eat anything except some beach side crunch treats, he literally is not eating anything not even canned food, he crys for treats but I’m not giving him these anymore. I’m completely stumped, not knowing what to fo.

    • I’m assuming you meant hyperthyroidism. While it’s important to protect the kidneys in a hyperthyroid cat, protein restriction isn’t indicated until the very late stages of kidney disease. This article may help: The botton line is that your cat needs to eat. If he’s not willing to eat anything, you need to contact your vet immediately.

  2. Bunch of nonsense. I’ve had thyroid disease myself and there are many similarities between human and animal thyroid disease. I had surgery and also radioactive iodine treatment in 1992 and 1993 when my right thyroid lobe was removed and found to contain cancer cells. There is no DIET that can cure thyroid disease, the disease has to be managed. You have to know the science behind it. In cats, tumors, usually benign, grow on the cat’s thyroid gland. The gland is located lower in the neck/chest area, so sometimes small bits of tissue from the thyroid tumors detach themselves from the gland and implant themselves in the cat’s chest wall. I am dealing with a cat with this right now–my third cat actually that has had this–and she’s lost half her body weight. We tried this stuff and she did not like the taste of it and her thyroid levels were very high. We went on Feline Methimazole and she’s now on 2 pills daily–one in the morning and one at night–hidden in Pill Pockets, so she gets the medication. I am looking into getting Radioactive iodine therapy for her (I-131) which will take care of the tumors on the gland as well as any tissue that has implanted itself in the chest wall. She was looking like she was going to die before I got the Pill pockets. They wanted me to try the Transdermal methimazole, which you rub into the inner part of the cat’s ear. That doesn’t work as well as the pills. She is starting to look better and put on weight but the tumors keep growing even with the pills, so you have to treat the disease. This claim about a thyroid cat food normalizing thyroid function is misleading and in my opinion, dangerous.

  3. My cat had terrible sneezing and mucus around the same time she began taking methimazol. We didn’t see the connection and put her on prednisolone and that didn’t help,tried Abiquiul. She has been off methimazol for 3 weeks and her sneezing is less. She had sneezing fits of 25x with mucus. So the vet suggests the radiation iodine.
    How can I absolutely know,methimazol caused these crazy symptoms. We tried other things to help with sinus and she eels better without methimazol. Feel anguish about putting this 13yr old cat through the radiation therapy and it is 2100.00. Will she survive it. She has a sensitive stomach so don’t want to take her off,her regular food. How long can she be off methimazol before possible heart or liver trouble begin?

    • Not treating a cat with hyperthyroidism will inevitably lead to complications down the road. As long as your cat is a candidate for the I131 therapy, I’d encourage you to consider it. You can read about my experience with it here:

  4. I appreciate all the comments on this post. However, I have a slightly different perspective. Our cat was diagnosed with HT about two years ago. One choice was to do radiation therapy. It was expensive. I was concerned about having a radiated cat after two weeks of treatment. I was concerned she might not even survive the treatment. So, our vet encouraged us to try the y/d diet. Since then, she has improved. Her coat is improved too. She didn’t take to the food easily. Sometimes she doesn’t eat well. I am sad to learn that people believe the diet is poor. I would like to supplement my cat’s diet. I found this post because I am looking for other things to feed my cat even though I do understand that the recommendation is to eat only this food.

  5. My female cat is 16 1/2 yrs old she was diagnosed today with hyperthyroid disease My question is can she have the one time treatment (I don’t care about the price) at this age… She is 4 lbs highest weight ever was 6 lbs and in good shape other than this Thank you for your feedback

    • It would be up to your vet to determine whether you cat is a candidate for the radioactive iodine treatment, Tere. It depends on her general health, and what shape her heart and kidneys are in. I have seen cats as old as yours and older go through the treatment without any problems.

    • September 16, 2016 my cat was diagnosed with hyperthyroidism a year ago. She is 14 years old. Taking methmazole daily, which effectively helped. But began having loose stools that stunk so badly. Decided by talking to our vet to try the y/d dry food for 3 months. Her stools were not loose anymore and I thought she was doing well. Unfortunately my cat went from 6lbs to 3lbs. (She has always been small) normal weight 8lbs. She stopped eating and drinking!! Nearly killing her. So, we stopped the y/d. Had blood work done. Her hormone levels were through the roof!! Force fed her the hills a/d diet and the next day she was eating it on her own. Totally transformed her. We’re back to taking methmazole. The y/d as far as I’m concerned is not a cure all.

  6. My calico was diagnosed HT a few years ago; thyroid levels were always high end of normal but she exhibited the other signs of HT (hyperactivity, increased appetite, weight loss, going outside litter box, etc.). I wanted her to undergo I131 treatment but was not recommended due to her “normal high” thyroid levels and non-palpable thyroid. She could not tolerate tapazole (broke out rashes, vomiting, etc.). She is now 15 and was on Hill’s Y/D for almost 10 months. She took well to the food (both canned and dry) and thyroid levels came back down to high normal, but she did not gain that much weight (2 lbs at most?). Last week she stopped eating. Vet did urine tests, blood work and nothing seemed wrong. We gave her several different types of food just to get her to eat something. She ate very little for couple days and vet thought her time might be up and we should consider euthanasia rather than let her starve. The last couple days, she started eating a bit more (canned Wellness chicken which she loved before Y/D). I’m so confused – follow vet’s advice to euthanize or let her continue eating other food to keep her going? Other than lethargy, she’s still affectionate, can walk, jump, using litter box, etc. In other words, not exhibiting signs of dying. Yes she is thin and her coat is not as it used to be, and I know cats mask pain, etc., but I’m so conflicted about what’s best for her at this point. Should I give her some more time?

    • Based on what you’re saying, I’d definitely give her more time. Given that all her lab work is normal, and she’s actually liking the Wellness chicken, I’d encourage her to eat a better quality diet, like the Wellness, or another high quality grain-free diet. There are many things you can do to encourage a cat to eat: pour some tuna juice over the food, sprinkle Parmesan cheese over it (yes, the stuff from the green can!), warm the food slightly. It certainly doesn’t sound to me like it’s time to give up. All my best to you and your kitty.

  7. Been giving our cat Ginger both dry and cannded Hills Prescription Y/D for three weeks.
    Hugh difference in our cats appetite. Have been pilling her for last 3 years and she still ate all the time and her bowels were horrible. After a few days her bowels were normal and her appetite has decreased and her heart rates has slowed, which we can tell by watching her breathing. She is resting more and eating less. I add a little hot water to some dry food then mix in a little canned food. She does well eating it. Now starting week four and I will stop pilling per vets advice and just give her Y/D food only, strickly nothing else per vets advice. Time will tell if the Y/D food is enough to control her hyperthryoidism. So far so good.

    • I would be very interested to hear from you again after your vet runs follow up bloodwork on Ginger, Brenda.

  8. Any so-called “veterinarian” endorsing and selling this species-inappropriate “food” should be up for not only fraud and mal-practice, but animal abuse.

    Allllll that education (at least 12 years of regular schooling, right?) and they are apparently not aware of the Physiology, anatomy, and biological makeup of the very creatures they go on to a “higher” education to study?

    And on top of it, their livlihood and very job is to EXAMINE these very same creatures!

    Carnassials (sp?) and fangs — NO grinding teeth; NO rotation in the jaws, up and down motion is all they are capable of and built by nature to do.

    If there are any fraud lawyers out there, you’ll have a verrrrrry easy time in a court because who’s gonna be able to prove that these animals aren’t CARNIVORES?

    • I wouldn’t go so far as calling selling prescription diets malpractice, CC, but it certainly doesn’t make much sense, given the physiology of an obligate carnivore. Until the nutrition curriculum in veterinary schools is no longer sponsored by petfood companies, you’re going to have a situation very similar to the relationship between medical schools, physicians and pharmaceutical companies. Thankfully, there are many veterinarians who are starting to educate themselves, on their own time, on species-appropriate nutrition for cats, and I have a lot of respect for them. Veterinary medicine is an ever changing discipline, and it’s hard to stay on top of everything all the time.

      • Thanks for your kind response, Ingrid :>)

        Agree about the Big Pharm influence, indeed. But it’s still not junk food. At least they have *some knowledge of medicine; side effects, how it works.

        Imagine an MD Pediatrician not only endorsing and selling corn chips to humans to feed their children, but “enforcing” this strict diet upon them? Then not disgnosing effects of such a strict diet objectively and honestly due to the conflicts of interest.

        Better analogy, “prescribing” a child eat raw meat because the cattle ranchers fund them so generously? Influence overrides common sense when it comes to our pets and we are vulnerable to the “pros” as our animals cannot tell us what hurts.

        I see no difference, as the child’s teeth and physiology aren’t those of a cat’s, not to mention the inevitable health issues which would be masked by the drugs and other “treatments”.

        Thanks for listening :>) =^..^=

  9. My vet suggested this for my almost 20-year-old m.e. lou, but the ingredients turned me off. m.e. lou also has renal failure. I use the transdermal Methimazole, and that works the best for her.

  10. Just one look at the ingredients for that diet or any of the Hill’s foods is enough to make me run screaming. Our Hyper-T girl Hemmie was managed with methamazole (she was great about being pilled), a raw diet and supplements for 5-6 years.

    • I can’t imagine feeding this diet either, Sally, even if it were to actually live up to the claims.

  11. Before any “diet” can work, you’ve got to get cats to eat it….. Angela would not go near either the wet or the dry y/d food…… I’ve been pilling her and she has gained her appetite back, thank God.
    We’ll see what the vet says in a couple of weeks.

    • This is not the first report I’ve heard that this diet is not all that palatable, Allia. All my best to Angela!

  12. We have quite a few hyperthyroid cats on this diet at our hospital and so far their thyroid levels have been in normal range.

    • What is your opinion regarding the long term effects of this diet and its effect on kidney function?

  13. All I could was roll my eyes when I heard they were coming out with a thyroid diet. I didn’t even bother to read the ingredients. Are you telling me their dry food is a vegetarian diet?? What on earth are they thinking?!?!?

    • I, too, was shocked by the complete omission of animal protein from the dry form of this diet, Connie.

  14. I’m not an expert on the regulations, but I suspect that if this were for humans, the FDA wouldn’t let them make such claims without more research (i.e. proof that this actually works).

    • I believe that human trials would be with much larger groups of subjects, and for longer periods of time, Anne.

    • Thorough, detailed explanation(s) here — Harvard Law student left no stone unturned:

  15. I’m not really a fan of “prescription food” because of the ingredients used. Cosmo *had* to be on the Royal Canin prescription food for FLUTD and I found him drinking copious amounts of water which was “good” but highly unnatural for a cat. I started to move him towards more canned food and ultimately to home cooked food. The kitties all eat high quality (no corn, no by-products) kibbles for breakfast and home cooked for dinner and are doing great! 🙂

    • You are an inspiration to all animal lovers. Taking care of your wonderful fur babies and sharing what you feed them is so caring.

      My poor kitty has thyroid disease, she has this for three years and is now going down hill so fast, I am using the prescription diet food for her but nothing is working. Sophie is 13 years old, she was doing so good, meds working for her for her Thyroid disease, she just stopped eating, we have had her everywhere, blood test, Kidney’s are good, her blood work is good, she does eat but not a lot and some days I am lucky if I can get her to eat at all.

      My vet gave us pills to help her want to eat but this is not working anymore, I am so upset and have to make a very hard decision for which I cannot bring myself to do just yet.

      What type of diet would you recommend, I know that this was two years ago you posted this but I hope you can share with me something that will help my Sophie.

      • I’m sorry your kitty is having such a hard time, Tish. You can find my recommendations for diets here:, but you’ll still need to give her the thyroid medication. You may also want to try some of these tricks to try to entice her to eat:

Leave a Reply

Your email address will not be published.