Canine Hypothyroidism Causes and Treatment

Originally published May 18, 2015

Doug on canine hypothyroidism
Doug the Dog Boss

Canine Hypothyroidism is the reduced function (hypo) of the thyroid gland. The thyroid is a butterfly shaped gland in the neck, on the trachea, and makes a hormone called thyroxine that controls metabolism. When the gland doesn’t make enough thyroxine, the dogs metabolism slows abnormally.

It’s a common disease in dogs that can affect all breeds, but it is most often found in medium to large breeds like Golden Retrievers, Doberman Pinchers, Irish Setters, Dachshunds, Boxers, Cocker Spaniels — and bulldogs. It usually occurs in middle-aged dogs (ages 4 to 10) and neutered males and spayed females are at a higher risk, though experts are not sure why. In most cases hypothyroidism is caused by your dog’s own immune system attacking his thyroid gland!

Symptoms of Canine Hypothyroidism

The most prominent symptoms are lethargy and weight gain for no apparent reason. Other indications include dark patches on the skin, often accompanied by hair loss and dry flaky skin. A slowed heart rate, increased incidence of ear infections, and an intolerance to cold, are also indications.

Other symptoms include severe behavioral changes such as unprovoked aggression, head tilt, seizures, anxiety and/or compulsivity and depression.


Canine hypothyroidism is a condition that is usually caused by an autoimmune disease. It occurs when a dog’s immune system attacks the thyroid gland, resulting in destroyed tissue (also called lymphocytic thyroiditis). This destruction results in abnormal gland function and a decline in the amount of hormone produced by the thyroid gland. Since this hormone regulates many body functions, dogs experience multiple symptoms such as hair loss, weight gain and lethargy. The disease rarely occurs before age 4, with an average age of 7. The incidence is 1 in every 250 dogs.[1]

One recent study has concluded that a dog who pulls hard or lunges against a collar can damage his thyroid and cause this disorder. If you have a dog that pulls or lunges, especially if he or she spends any time on a tether, be sure you use a harness, not a collar with the tether.


Diagnosis is normally done by having your veterinarian run a blood panel.

The good news is that this disorder is easily treatable with a pill containing a man-made replacement hormone. While treatment will continue through daily treatments for the rest of the dog’s life, the medicine is inexpensive and readily available. Several blood tests may be needed to find the correct dosage level to correct the hormone deficiency, but once that is done your dog will be able to live a happy, normal life.

If your dog has gained a significant amount of weight, getting rid of that will be your first priority. Cochise has been working hard to get back to his normal, buff, self.

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