Hyperthyroidism is primarily a middle-aged or older cat disease. Although it's multi-factorial, a common presentation is a benign nodule/enlarged thyroid gland (which may or may not be palpable by a veterinarian).


Cats with hyperthyroidism more often than not also have concurrent chronic kidney insufficiency, diabetes, heart disease, and/or hypertension. This makes treatment of hyperthyroidism rather tricky in allopathic terms. However since holistic options such as homeopathy look at the entire body, not just bits and pieces, it's very much treatable based on the cat's symptom picture.


Not all cats exhibit symptoms, and not all have the "classic" symptom of being ravenous all the time but without weight gain (even loss in some cases). Common symptoms include fur loss, excessive vocalization, weight loss, muscle deterioration, heat/cold/extreme temperature intolerance, crankiness, chronic vomiting, and chronic diarrhea. Also, the cat's fur doesn't quite lie flat, and can appear dull and greasy. In some cats, there is thinning of fur around the eyes and ear area accompanied sometimes with scratching.


If thyroxine (T4) value is below 2.0 ug/dl, then barring existence of some other serious disease depressing T4 levels, no matter the age of the cat, one can rule out hyperthyroidism. On the flip side, if the total T4 level is above 4.0 ug/dl, that's a pretty clear-cut case of an overactive thyroid gland. Please note that Idexx and Antech have different top # for the range, but it's still an absolute measurement, so to me it makes sense to still start questioning when the T4 gets above 2.5 or so.

Where it gets tricky is that grey zone of low to mid 2ish and above especially in an older cat. Since diseases such as diabetes, cancer, and CRF can depress T4 levels (see reference below), a cat above age 8 or thereabouts with even a "normal" T4 # can be hyperthyroid.

Because I'm a lifelong homeopathy student, I consider symptoms to be extremely important. I've never seen a cat exhibit what I consider classic hyperthyroid symptoms, and have some other issue. Frequently it's hyperthyroidism and something else that is often masked by it e.g. CRF, diabetes. So I go by symptoms not just T4 (sometimes also free T4). Quite often, liver enzymes – ALT and AST – are elevated as well. An added confirmation of the benign tumor (adenoma) on one or both of the cat's two thyroid glands is even better of course.

Determining whether a cat is hyperthyroid or not can be really challenging because additional tests e.g. free T4 (fT4) of cats in the so-called grey zone of 2.5 - 4 aren't necessarily reliable either. The free T4 test has been known to show false positive results for many reasons ranging from sample collection, storage, and temperature issues to existence of non-thyroid illness e.g. IBD and CRF. Please read this caution from Antech, and these notes about a low to normal T4 accompanied by elevated fT4 before you assume your cat is hyperthyroid.

While I'm not a vet, I have seen hundreds of people wrestle with this issue over the almost 11 years we've been around in cyberspace. I'd say this - before you assume it's hyperthyroidism, re-test T4 in 4-6 weeks. T4 levels can and do fluctuate even in the same day (Peterson et al's paper referenced below), which is why vets will often recommend this option as well.

I've seen cases where the T4 # went from 3 to 2 in a matter of 1-2 weeks. If T4 is still "high" (this can be a judgement call depending on cat's age), a reliable facility is being used, and your cat doesn't have any other illness you know of, then a Free T4 is a good idea.

Bottom line - barring other health issues, if both T4 and fT4 are high, one can be a bit more sure about overactivity of the thyroid gland. Add in symptoms, adenoma, and elevated liver enzymes, and the picture becomes a bit clearer. Unfortunately I've known of far too many cats who are hyperthyroid and aren't being treated, as well as those that aren't but are being given Tapazole despite high fT4 for non-thyroid reasons.


Various things have been fingered as having possible goitrogenic effects accounting for the high incidence of hyperthyroidism in domestic cats since the 1970s.

In one study, they found that indoor cats were 11 times more likely to be hyperthyroid than outdoor cats. There's nothing outdoors that would protect a cat from hyperthyroidism, so makes sense that there's something we're doing inside that increases a cat's risk factors - environment (like they found in the New Zealand study listed below) with sleeping on the floor, yucky flea products etc, and of course food especially canned. No, not so fast! This doesn't mean kibble is okay, no way!

Another paper posited that pop-top aluminum cans in particular could be to blame. Such cans are lined with a substance called Bisphenol-A (BPA); the substance also mixes in with the fat in canned food and enters cats' bodies. The jury's still out on whether this was more of a correlation issue or some caustive factors are at play here. Meanwhile just recently this issue of BPA in plastic bottles has come to the forefront, so perhaps we shouldn't pooh-pooh the possibility that BPA could mess with cats' endocrine receptors. It's certainly not something we want in their bodies, ugh.

The most recent and groundbreaking study by Dr. Janice A. Dye of the EPA and her university colleagues puts the blame squarely at polybromated diphenyl ethers (PBDE) from bromated flame retardants in our clothing, upholstery, etc. Hyperthyroid cats had much higher levels of PBDE in their blood, which isn't a surprise because in addition to this environmental assault, Prof. Dye et al found that found that fish/seafood flavors of canned food had higher PBDE content than dry as well as non-seafood canned foods.

PBDEs have a chemical structure that is very similar to dioxin and PCBs, which are two other known endocrine disruptors:( There's no way this is a good thing, even if not everyone is convinced PBDEs are implicated in overactivity of cats' thyroid glands.

Bottom line - cats are exposed to household dust full of chemicals, so we should vacuum often, and do our level best to live a clean toxin-free life for our own good as well as for our cats' welfare. Similarly it's a no-brainer to avoid nasty flea meds and chemicals are harmful to cats. If you feed canned food, transfer the contents immediately to airtight glass jars (Note: canning jars do have BPA on the outer edge of the inside lid, so it's hard to escape the stuff!). Even better, feed a raw diet so you can be in control Innocent


Herbs need to be customized because a hyperthyroid cat with diabetes might benefit from a diffrerent individual herb or set of herbs than one with CRF or other issues. The response to various herbs e.g. Bugleweed, and Motherwort has been spotty and not all cat caregivers have reported back with their experiences in terms of either side-effects (or lack thereof) or change in T4 levels.

There are other safe herbs that can be useful e.g. Astragalus and Lemon Balm but along with other herbs, aren't a one-size--fits-all option. My best results have been with either homeopathy alone, or just a few carefully chosen single herbs that address not just the thyroid but that cat's specific issues be it diabetes or CRF or HCM along with use of the following supplements.

Supplements on the other hand, have been used successfully by a lot of cat caregivers on the list. Some examples:

  • Glandulars - although thyroxine (T4) is removed from thyroid glandular products, please call the company first to make absolutely sure. One product that has been used a lot with my list cats is Thytrophin PMG by Standard Process. Depending on what other issues your cat has, other glandulars might also be helpful e.g. cardiac or renal glandulars.
  • CoQ10 30mg minimum, preferably 50mg daily - CoQ10 levels are lowest in humans with heart and also hyperthyroid issues. It also has been found to help the kidneys (see reference in CRF article), something with which many cats with hyperthyrodism could use help.
  • L-Carnitine - 250-500mg for both heart and thyroid; this one build up slowly because it can give some kitties the runs. It also has a citrus taste many cats dislike, yet others don't seem to notice it, so cat mileage varies. References to 2 papers below.

If you're interested in a health, behavior, and/or diet consult, please click here.


"Chronic renal failure can suppress total T4 concentrations in cats with concurrent hyperthyroidism, and free T4 is not a useful distinguishing test." Cathy E. Langston DVM, and Nyssa J. Reine DVM, " Hyperthyroidism and the Kidney", Clinical Techniques in Small Animal Practice, Volume 21, Issue 1, February 2006, Pages 17-21
M E Peterson, T K Graves, I Cavanagh "Serum thyroid hormone concentrations fluctuate in cats with hyperthyroidism", J Vet Intern Med.;1 (3):142-6
Krista M. Martin, MPH; Mary Anne Rossing, DVM, PhD ; Lennox M. Ryland, DVM, MPH; Ronald F DiGiacomo, VMD, MPH; William A. Freitag, DVM, "Evaluation of Dietary and Environmental Risk Factors for Hyperthyroidism in Cats", J Am Vet Med Assoc 217[6]:853-856 Sep 15 '00
American Chemical Society (2007, August 16). Cat Disease Linked To Flame Retardants In Furniture And To Pet Food. ScienceDaily.
Olczak, J.; Jones, B.R.; Pfeiffer, D.U.; Squires, R.A.; Morris, R.S.; Markwell, P.J., " Multivariate analysis of risk factors for feline hyperthyroidism in New Zealand", New Zealand Veterinary Journal, Volume 53, Number 1, February 2005 , pp.
Charlotte H. Edinboro , DVM, PhD J. Catharine Scott-Moncrieff , VetMB, MS, DACVIM Evan Janovitz , DVM, PhD, DACVP H. Leon Thacker , DVM, PhD, DACVP Larry T. Glickman , VMD, DrPH, "Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats", Journal of the American Veterinary Medical Association, March 15, 2004, Vol. 224, No. 6, Pages 879-886
Philip H. Kass, Mark E. Peterson, Julie Levy, Katherine James, David V. Becker, Larry D. Cowgill (1999) Evaluation of Environmental, Nutritional, and Host Factors in Cats with Hyperthyroidism, Journal of Veterinary Internal Medicine, 13 (4) , 323–329

In this paper, they found support for the fact that L-carnitine (LC) increases glutathione (GSH) levels; they also report a lowering of creatinine levels. It is hard to extrapolate whether non-gentamicin treated animals would also benefit from LC's protective effects in terms of necrosis and degeneration in the proximal tubules of renal cortex (pg 4):
A. Kart, K. Yapar, M. Karapehlivan, R. Tunca, M. Ogun and M. Citil, "Effects of L-Carnitine on kidney histopathology, plasma and tissue total sialic acid, malondialdehyde and glutathione concentrations in response to gentamicin administration in Balb/C mice", Revue Méd. Vét., 2006, 157, 4, 179-184

These authors found that "that it inhibits thyroid hormone entry into the nucleus of human and animal cells (fibroblasts, hepatocytes, neurons), thus explaining the peripheral antagonism" and conclude that "carnitine would be useful both for the prevention and the therapy of the thyroid storm.":
Salvatore Benvenga, Rosaria M. Ruggeri, Antonia Russo, Daniela Lapa, Alfredo Campenni and Francesco Trimarchi, "Usefulness of l-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized,double-blind, placebo-controlled clinical trial." J Clin Endocrinol Metab. 2001, Aug;86 (8):3579-94.