Home Thyroid Disease

Thyroid Disease in Dogs

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • Hypothyroidism is the common thyroid problem in dogs, treated with a daily tablet for life.
  • Hyperthyroidism is rare in dogs and usually comes from a tumor, food or too much medicine.
  • Raw diets with head or neck meat, gullets, some jerky and some canned all-meat foods can contain thyroid tissue.
  • Diet-related hyperthyroidism clears within about a month of stopping the food.
  • A low T4 alone isn't enough to diagnose hypothyroidism.

Table of Contents

Research Types Hypothyroidism Tests Hyperthyroidism Diet Skin and odor FAQ Sources

Dog Hormonal Disorders Quicklinks

Adrenal Glands Addisons Disease Cushings Disease Dog Diabetes Pancreatitis Thyroid Disease

Thyroid disease in dogs is usually hypothyroidism, an underactive thyroid that slows the body down. It's common in middle-aged, medium and large dogs, and it's treated with a daily thyroid hormone tablet for life.1,2,3 An overactive thyroid (hyperthyroidism) is rare in dogs. When it happens, the cause is usually a thyroid tumor, or something in the diet such as raw meat, jerky or canned food containing thyroid gland tissue. Too much thyroid medicine can do the same.1,4,5,6 Diet-related cases clear up within about a month of changing food.4,5

See a vet now if your dog:

  • Collapses, has a racing heart, or pants heavily or struggles to breathe at rest, especially if on thyroid medicine or eating raw food, jerky or a canned all-meat food7,8,9
  • Has eaten a bottle of thyroid tablets. Call your vet or an animal poison helpline now; most dogs do well with prompt care.9

A new lump in the neck needs a vet visit within days.1 See thyroid cancer in dogs.

What the Research Says

  • About 1 in 435 dogs has hypothyroidism, and about 1 in 2,500 is newly diagnosed each year. In a UK study of 905,553 dogs, Dobermans had 17 times the odds of crossbreeds, followed by Tibetan Terriers, Boxers and Alaskan Malamutes.3
  • A low T4 alone isn't enough. Illness and some medicines lower thyroid levels, and hypothyroidism is thought to be one of the most overdiagnosed diseases in dogs.2
  • Pet food can cause hyperthyroidism. FDA investigations from 2016 to 2018 found 17 dogs with excess thyroid hormone from jerky treats and canned foods made from beef or bison. Five foods were recalled.4
  • Diet-related cases reverse. In 14 dogs eating all-meat foods or treats, thyroid levels were normal in every dog at least 4 weeks after the food was stopped.5

Types of Thyroid Disease in Dogs

ConditionHow commonMain causesMain signs
Hypothyroidism (underactive)Common3,10Immune destruction of the gland (thyroiditis) or gland shrinkage, over 95% of cases2,1Weight gain, lethargy, seeking warmth, thin coat, skin and ear infections1,11
Hyperthyroidism (overactive)Rare12,1A thyroid tumor, thyroid tissue in food, or too much thyroid medicine1,4,6Weight loss, big appetite, restlessness, panting, thirst, fast heart rate1,7
Thyroid tumorsUncommonUsually cancer (carcinoma)13A lump in the neck; most don't change hormone levels13,14

Hypothyroidism: The Basics

Most cases happen at 4 to 10 years of age in medium and large breeds. It's uncommon in toy breeds.1,2,3 Golden Retrievers, Dobermans, Irish Setters, Cocker Spaniels and Boxers are among the breeds often listed.2,11,3 Signs develop slowly:1,11,6

  • Weight gain without eating more, and lethargy or less interest in exercise
  • Seeking warm places
  • A dry, dull or thin coat, hair loss on both sides of the body or the tail that usually doesn't itch, and slow regrowth after clipping
  • Darkened skin and repeated skin or ear infections

Treatment is synthetic thyroid hormone (levothyroxine) given daily for life. FDA-approved tablets for dogs are available.2,15 Energy usually improves within about 2 weeks; the skin and weight can take up to 3 months.2 With treatment, dogs have a normal life expectancy.6,16 For the full guide, see hypothyroidism in dogs.

Thyroid Tests in Plain Words

TestWhat it showsWatch out for
Total T4A screening test. A normal result makes hypothyroidism unlikely2Low in sick dogs, on some medicines (such as steroids and some seizure medicines) and in Greyhounds and other sighthounds2,1
Free T4 (by equilibrium dialysis)A more specific confirmation2,16Can still be lowered by illness
TSHHigh TSH with low T4 supports hypothyroidism2Normal in 20% to 40% of truly hypothyroid dogs, and raised in some sick dogs2
Thyroglobulin antibodiesShows the immune system is attacking the gland2Only about a third of dogs with high levels go on to develop hypothyroidism2
Full panel including T3Helps spot diet-related or medicine-related hyperthyroidism17,4Dogs eating thyroid tissue in canned food can show low T4 with high T34

If your dog is unwell with another illness, your vet may wait until it resolves before testing.2 See blood tests for dogs.

Hyperthyroidism in Dogs

From food and treats (dietary hyperthyroidism)

Foods and treats made with beef or bison necks (gullets) or head meat can contain thyroid gland tissue, which carries thyroid hormone.7,8 Raw diets, jerky treats and some canned all-meat foods have been linked to cases.4,5,18

  • Signs: more thirst and urination, weight loss despite a good appetite, restlessness, heavy panting and a fast heart rate. Some dogs show no signs.17,7,18
  • Diagnosis: thyroid tests (dogs eating canned foods may show a normal or low T4 with a high T34), and a diet history that includes these foods. Tell your vet everything your dog eats, including treats and chews.17
  • Treatment: stop the food. Thyroid levels usually return to normal within about 2 to 6 weeks, most often by a month.4,5,17,12,19 Untreated, the extra hormone can damage the heart.7

If you suspect a food, your vet can report it to the FDA.17

From too much thyroid medicine

Too high a dose of thyroid hormone can cause weight loss, hyperactivity, more drinking and panting.6 That's one reason for regular blood tests. A one-time accidental overdose is usually less serious than a long-term excess, but call your vet or a poison helpline.9

From a thyroid tumor

About 1 in 10 to 1 in 5 thyroid tumors makes too much hormone; most don't change thyroid levels.14,13 When hyperthyroidism comes from a tumor, the outlook is more guarded, and treatment may include surgery, radioactive iodine or radiation.1 See thyroid cancer in dogs.

Diet and Thyroid Disease

No special diet treats hypothyroidism, and the veterinary references we reviewed recommend none. Feed a complete and balanced food and keep your dog at a healthy weight. Claims that soy or gluten cause thyroid disease in dogs aren't backed by good evidence. In a trial of 20 dogs, a high-soy diet had no overall effect on thyroid hormones, though one thyroxine measure rose slightly.20 The real diet risk is the opposite problem: foods or treats that contain thyroid gland tissue.4,5 Ask your vet whether to give the thyroid tablet at the same time relative to meals each day.2

Skin Problems and Odor in Dogs With Hypothyroidism

Hypothyroidism itself usually causes hair loss that doesn't itch, but it makes dogs prone to bacterial and yeast (Malassezia) skin and ear infections, which can itch and smell.11,2,21,22 Hormone disease is one of the most common causes of greasy, scaly skin (seborrhea), which can have a strong odor.23 These infections tend to come back until the thyroid level is right and other causes, such as allergies, are controlled.22,23 Skin tape or swab tests show your vet whether yeast or bacteria are involved.22,6 See yeast infections in dogs and skin infections in dogs.

Frequently Asked Questions

What is the life expectancy of a dog with hypothyroidism?

With daily thyroid hormone and regular checks, dogs with hypothyroidism have a normal life expectancy. It's treatable but not curable.

What are the first signs of thyroid problems in dogs?

For an underactive thyroid: weight gain without eating more, tiredness, seeking warmth and a thin, dull coat. For an overactive thyroid: weight loss, a big appetite, restlessness, panting and drinking more.

Which dog breeds get thyroid problems?

Medium and large breeds are affected most, especially Dobermans, Golden Retrievers, Boxers, Irish Setters and Cocker Spaniels. It's uncommon in toy breeds.

What should I not feed a dog with thyroid problems?

Avoid raw meat, gullets, head meat and jerky or all-meat foods that may contain thyroid tissue. No ordinary food is proven to cause or worsen hypothyroidism.

Can dogs get hyperthyroidism?

Yes, but it's rare. It's usually caused by a thyroid tumor, thyroid tissue in food or treats, or too much thyroid medicine.

How often does a dog on thyroid medicine need blood tests?

Usually about 4 to 8 weeks after starting or changing the dose, then once or twice a year once the dose is right.

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Sources and further reading

This article was rewritten and fact-checked on October 30, 2026 against current veterinary references and specialist guidelines:

  1. Peterson ME, DVM, DACVIM; Kritchevsky JE, VMD, DACVIM. Disorders of the Thyroid Gland in Dogs. Merck Veterinary Manual (pet owner version), full review June 2018, last updated September 2024.
  2. Heseltine J. Hypothyroidism in animals. Merck Veterinary Manual, May 2025.
  3. Geddes RF, O'Neill DG, Khoo JSP, et al. Frequency, breed predispositions and other demographic risk factors for diagnosis of hypothyroidism in dogs under primary veterinary care in the UK. Canine Medicine and Genetics, 2022 (VetCompass study).
  4. Rotstein D, Jones JL, Buchweitz J, Refsal KR, et al., Reimschuessel R. Pet food-associated dietary exogenous thyrotoxicosis: retrospective study (2016-2018) and clinical considerations. Topics in Companion Animal Medicine 43:100521, 2021.
  5. Broome MR, Peterson ME, Kemppainen RJ, Parker VJ, Richter KP. Exogenous thyrotoxicosis in dogs attributable to consumption of all-meat commercial dog food or treats containing excessive thyroid hormone: 14 cases (2008-2013). Journal of the American Veterinary Medical Association 246(1):105-111, 2015.
  6. Boldan M, DVM. Hypothyroidism in Dogs. PetMD, September 29, 2026.
  7. FDA issues warning about thyroid hormones in pet food and treats. dvm360, April 5, 2017.
  8. Zeugswetter FK, Vogelsinger K, Handl S. Hyperthyroidism in dogs caused by consumption of thyroid-containing head meat. Schweizer Archiv für Tierheilkunde 155(2):149-152, 2013.
  9. DeClementi C, VMD. Acute thyroid hormone supplement overdosage. Veterinary Medicine (ASPCA Animal Poison Control Center Toxicology Brief), June 2001.
  10. Panciera D. Canine hypothyroidism. Veterinary Focus 27(2), June 2017 (hosted by IVIS).
  11. Cornell Riney Canine Health Center. Hypothyroidism. Cornell University College of Veterinary Medicine.
  12. Główny D, Sowińska N, Cieślak A, Gogulski M, Konieczny K, Szumacher-Strabel M. Raw diets for dogs and cats: potential health benefits and threats. Polish Journal of Veterinary Sciences 27(1):151-159, 2024.
  13. Liptak JM. Head and neck tumors: thyroid carcinomas. AnimalCancerSurgeon.com, updated March 6, 2017.
  14. Falcão S. Hyperthyroidism in two dogs with a functional thyroid gland carcinoma. SEVC Annual Conference, Barcelona, 2013 (hosted by IVIS).
  15. U.S. Food and Drug Administration. FDA approves ThyroKare (levothyroxine sodium tablets) for replacement therapy for diminished thyroid function in dogs. CVM Update, January 2021.
  16. Weir M, Williams K, Ward E. Hypothyroidism in dogs. VCA Animal Hospitals, 2024.
  17. AVMA News. Thyroid hormones in food sicken dogs. JAVMA News, American Veterinary Medical Association, April 26, 2017.
  18. Cornelissen S, De Roover K, Paepe D, Hesta M, Van der Meulen E, Daminet S. Dietary hyperthyroidism in a Rottweiler. Vlaams Diergeneeskundig Tijdschrift 83, 2014.
  19. Dodds WJ, DVM. Myths about thyroid disorders, vaccines in pets. Veterinary Practice News Canada, June 23, 2016 (opinion).
  20. Cerundolo R, Michel KE, Court MH, Shrestha B, Refsal KR, Oliver JW, Biourge V, Shofer FS. Effects of dietary soy isoflavones on health, steroidogenesis, and thyroid gland function in dogs. American Journal of Veterinary Research 70(3):353-360, 2009.
  21. Moriello KA. Pyoderma in Dogs. Merck Veterinary Manual (pet owner version), updated September 2024.
  22. Bond R, Morris DO, Guillot J, et al. Biology, diagnosis and treatment of Malassezia dermatitis in dogs and cats: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology, 2020.
  23. Heinrich NA. Seborrhea in Animals. Merck Veterinary Manual, updated May 2025.

About this article

Last updated : fully rewritten using the Merck Veterinary Manual, a VetCompass study of 905,553 dogs, FDA investigations of pet foods, published case series, Cornell University, PetMD and IVIS-hosted proceedings; added the research summary, thyroid disease types table, thyroid tests table, a section on hyperthyroidism from food, diet guidance, key takeaways and FAQ.

This page is for general information and is not a substitute for an exam by your veterinarian.