Hypothyroidism is the clinical condition caused by a deficiency of the thyroid hormone. The thyroid hormones are produced by the thyroid glands, which are located in the neck on either side of the trachea. Thyroid hormones are critically involved with the metabolism of most of the organs in the body. A deficiency results in a decreased metabolic rate, which may cause a wide variety of symptoms. Hypothyroidism generally affects middle-aged to older animals.


Symptoms will vary from dog to dog and can affect multiple organ systems and usually have a gradual onset. The most common signs are lethargy, mental depression, exercise intolerance, weight gain, hair loss of the tail, dry/oily skin, darkening of the skin, slow heart rate, and seizures.


 Dogs with hypothyroidism are easily treated with synthetic thyroid hormone supplement (i.e. l-thyroxine, T4) usually administered once to twice daily. Once the proper dosage has been established, yearly blood checks are recommended to insure continued adequate supplementation. Improvement of clinical signs can occur within one week of initiating therapy for mentation or take several months for hair regrowth. Lifelong thyroid supplementation is required for all dogs with a confirmed diagnosis of hypothyroidism.


 Hypothyroidism, like hyperthyroidism, is a disease that cannot be prevented. Annual examinations and lab work are the best ways to stay in touch with your pet’s overall health.