Dog News

Canine Hypothyroidism

by Shawn Finch, DVM

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The thyroid gland is a bilobular organ next to the trachea on the underside of the neck.  Each lobe is the shape, consistency, color and size (in a medium-sized dog) of a Swedish Fish, which from here on should be included on the candy’s packaging, because how cool is that??

The thyroid gland produces hormones that control the speed of the body’s metabolism.  As important as it is, you would never notice it was there unless it started underproducing or overproducing thyroid hormones.  Everyone (with bones) has one.

In canine hypothyroidism, the immune system destroys part of the thyroid gland, and it is unable to produce as much thyroid hormone as the body needs and the metabolism slows down.  The most common sign of an underactive thyroid gland is unexplained weight gain.  Low thyroid levels also may cause poor hair coat and skin health, the inability to stay warm, fatigue and even depression.

Dogs Prone to Hypothyroidism

Hypothyroidism is typically diagnosed in middle aged dogs.  Larger dogs develop the disease more often than smaller dogs.  Any breed or mix can develop the disease, but it is more common in some breeds than others.  The ten breeds most commonly diagnosed with hypothyroidism can be found on the Vet Info website.  An extensive list of breeds prone to hypothyroidism can be found in an excellent active registry by Michigan State University.

Cats and Dogs

Dogs with thyroid issues (almost) always have underactive thyroid glands which cause lower than normal metabolism and the disease called hypothyroidism.  Cats with thyroid issues (almost) always have overactive thyroid glands which cause higher than normal metabolism and the disease called hyperthyroidism.

And Now Back to Dogs…

Canine hypothyroidism is usually straight forward to diagnose and treat.  If the disease is suspected, thyroid hormone levels are measured with a simple blood test.

The kicker is that any illness can cause decreased thyroid levels without primary thyroid disease actually being present.


Sick euthyroid – having low thyroid levels caused by an illness other than hypothyroidism

When dogs are ill, we try to address all other issues and bring them back optimal of health before searching for a hypothyroidism diagnosis.  This may be a problem if the primary issue could be hypothyroidism OR something else.  If we test for low thyroid levels and find them, do we keep looking or have we found the primary problem?  As with so many other things in medicine, “it depends.”

Another potential snag is that some hypothyroid dogs do not show low thyroid hormone levels on blood tests.    Most do though.  If thyroid hormone levels are normal on initial screening tests but hypothyroidism is still suspected, more exhaustive testing can be done.


Treatment for hypothyroidism is an synthetic thyroid hormone replacement medication called levothyroxine.  The dose is determined based on the dog’s size, and the medication is given orally twice a day for life.  Thyroid testing is usually done every several weeks until thyroid levels and clinical signs are stable, and then thyroid levels are tested every six to twelve months.  Prognosis for a hypothyroid dog on medication is great.

What Has Been Your Experience With Canine Hypothyroidism?

Hypothyroidism is fairly common in dogs.  I have diagnosed and treated many patients, but never had a dog of my own with the disease.  If you have, can you share your wisdom here, especially for other pet lovers starting on the hypothyroidism journey with their own dog?  Was diagnosis straight forward?  What signs tipped you off that something was wrong?  Has regulation been easy or hard?  Is twice daily medication an issue?  What else should other dog lovers know about the disease?

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May your healthy pets stay healthy, and may your hypothyroid pets be as healthy as healthy pets!

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