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Hypothyroidism in Dogs

Date Published: 11/24/2003
Date Reviewed/Revised: 08/08/2018

What Is Hypothyroidism?

Hypothyroidism (underactive thyroid) results from decreased thyroid hormone production by the thyroid glands, which are located in the neck near the voice box. It is seen most commonly in middle-aged to older dogs. Affected dogs become easily fatigued, sleep for longer periods of time, are often dull in their attitude and may seek a warm area in cold weather. Slim breeds of dogs may seem puffy or over-weight, as the skin becomes thickened in hypothyroidism. The hair coat becomes dry and loses sheen, the color dulls and the hair may become very sparse, especially in areas of friction, with darkening of the skin. Clipped hair may not regrow. Affected dogs may become prone to skin infections and poor wound healing, as well as many internal health problems.


Diagnosis of hypothyroidism depends on taking blood samples to measure hormone levels. Tests may include measuring total T4, free T4, TSH or a TSH stimulation test. In some cases, diagnosis can be difficult and repeated testing is necessary.


Treatment is by administration of oral thyroid hormone supplementation. There is generally a rapid improvement in your pet's activity once treatment is started. However, determining the right dosage of the thyroid supplement can take time.  Additionally, regrowth of the hair and lightening of the skin may take several months. Occasionally, a pet may experience sensitivity to the amount of thyroid supplementation given. Signs associated with this include a rapid heart rate, increased water consumption or urination, change in temperament, or weight loss. Please contact your veterinarian if any of these signs occur. Hypothyroidism treatment is life-long because there is no true cure. Blood tests to measure hormone levels will need to be performed regularly to ensure that your dog is getting enough thyroid hormone supplement.