Hypothyroidism (Underactive Thyroid Gland) in Dogs

Hypothyroidism (Underactive Thyroid Gland) in Dogs

Animals Affected

Hypothyroidism is common in middle-aged and older dogs.


Hypothyroidism is a disease of the thyroid gland. The thyroid gland, located in the neck, produces a hormone called thyroid hormone. Although thyroid hormone plays a complex role in the body, its main effect is to increase the rate of metabolism. Hypothyroidism causes reduced production of thyroid hormone. Therefore, the main problem in hypothyroidism is reduced metabolism.


Symptoms of hypothyroidism include:

  • Weight gain
  • Skin problems
  • Decreased ability to exercise
  • Apathy and amotivational syndrome (frequently reported as “laziness”)
  • Behavior and personality changes

Risk Factors

Age is the primary risk factor.  Some breeds (most notably  Doberman Pinschers) suffer a high rate of hypothyroidism.


Untreated hypothyroidism can lead to obesity, arthritis and mobility problems, and chronic skin disease.


Diagnosis of hypothyroidism is made by interpretation of blood and urine tests in combination with assessment of clinical symptoms. Reliance on tests alone leads to over-diagnosis of the disease. Concurrent illness or treatment with common medications such as prednisone, carprofen (Rimadyl®), deracoxib (Deramaxx®), or phenobarbital will cause blood thyroid levels drop, leading to blood test results that mimic hypothryoidism. Therefore, dogs should not be treated for hypothyroidism unless they show clinical symptoms of the disease.


Hypothyroidism is easily treated with oral thyroid hormone supplement called levothyroxine. This is most commonly administered in pill form once or twice daily. Name brands of levothyroxine include Soloxine® and ThyroTabs®.


Regular monitoring of weight, clinical symptoms, and blood thyroid levels are necessary in dogs with hypothyroidism. Each dog responds differently to levothyroxine, so initial treatment may involve several rounds of medication adjustments followed by testing. The disease may progress over time, requiring occasional medication adjustments.


As mentioned, hypothyroidism is over-diagnosed in dogs, especially those on chronic medication, or those with other diseases.

Hypothyroidism is essentially unheard of in cats.

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The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.