Hypothyroidism in Dogs: Causes, Symptoms & Treatment

Hypothyroidism in Dogs: Causes, Symptoms & Treatment

Author WDF Staff


Hypothyroidism is a common health issue in dogs. The thyroid gland is located in a dog’s neck and it is one of the most important glands in the body. When the thyroid gland doesn’t produce enough of the necessary hormones (especially the hormone thyroxine), it causes the dog’s metabolism to slow. This is called hypothyroidism. Simply, the thyroid gland is producing hormones that control the process of turning food into fuel that keeps the dog’s metabolism going and when the thyroid gland is not working properly the metabolism slows down and this slower metabolism put almost every organ in the body in danger.

Dog breeds

This disease is common in dogs and it affects all breeds. However, in some breeds, this disease is seen more often. Some of the breeds prone to hypothyroidism are Golden Retriever, Irish Setter, Doberman Pinscher, Dachshund, Boxer, Cocker Spaniel, Brittany Spaniel, Airedale Terrier, etc. Researches show that hypothyroidism is more commonly seen in mid-to large-size breeds, and it occurs usually in middle-aged dogs (ages 4 to 10). Hypothyroidism is rare in the toy and miniature breeds.

FUN FACT: Spayed females appear to have a higher risk of developing hypothyroidism than intact ones. 


Although it cannot be cured, hypothyroidism is not life-threatening and with proper medication it can be managed and kept under control. The treatment is daily and life-long and it consists of oral administration of thyroid replacement hormone. Doses of thyroid replacement hormone are specific to each dog, and based on the dog’s weight and thyroid levels. It is important to treat the disease with proper medication because otherwise the disease will affect dog’s quality of life.


The most common symptoms of this disease are inexplicable weight gain, lethargy, muscle loss, dull, thin coat that sheds excessively, hair loss (primarily over the body), slow heart rate, increased dark pigmentation of the skin (especially in areas of friction), toenail and ear infections, and intolerance to cold.


Hypothyroidism in dogs is usually caused by one of two diseases: lymphocytic thyroiditis (when dog’s immune system attacks the thyroid gland) or idiopathic thyroid gland atrophy. 90% of the time, hypothyroidism is the result of lymphocytic thyroiditis.

Hypothyroidism in dogs - test

There are several blood tests to diagnose hypothyroidism. The most common screening test is a total thyroxine (TT-4) level in a blood sample. A low level of thyroxine is suggestive of hypothyroidism.

It is recommended to routinely evaluate thyroid functions for any dog over 4-5 years of age.

There is also another disease caused by a malfunction of a thyroid gland and that disease is called hyperthyroidism. Hyperthyroidism is when the thyroid gland produces too much of the hormone thyroxine, accelerating dog’s metabolism, causing rapid or irregular heartbeat, weight loss, increased thirst and urination, diarrhea, vomiting, enlargement of thyroid gland, etc. Cancer called thyroid carcinoma is the primary cause of hyperthyroidism in dogs.

If you suspect your dog suffers from hypothyroidism (or hyperthyroidism), if he is showing symptoms of the disease, take him to the vet immediately. Your veterinarian will perform necessary tests and then proscribe your dog proper medication.

World Dog Finder team

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