The thyroid gland produces important hormones that regulate metabolism, stress, reproduction and other critical functions. When that gland is under-producing, the resulting disease is called hypothyroidism. Signs of hypothyroidism in dogs can include sluggishness, a dull coat, slow heart rate, and weight gain. The good news is that it’s easily treated with synthetic thyroid hormone supplements.


Hypothyroidism is a very common disease in which normal thyroid hormone levels are decreased. It happens either because of a progressive deficiency of thyroid hormone (usually due to an autoimmune-related destruction of the thyroid gland known as lymphocytic thyroiditis) or, rarely, because of a congenital disease process (one that’s present from birth).

Hypothyroidism in its non-congenital (acquired) form is commonly reported in dogs. It is a highly treatable disease that affects multiple organ systems and can progress in insidious ways.

Signs and Identification

Most affected dogs display very subtle signs. Among these vague signs include lethargy, skin and coat abnormalities, and a heightened susceptibility to infection. Hair coat abnormalities include dry, scaly, itchy, or greasy skin. Additionally, a slow heart rate (bradycardia), dullness, cold avoidance, infertility, constipation, and (most typically) weight gain can become evident.

During basic screening, standard bloodwork findings can include hypercholesteremia (high serum cholesterol) and mild anemia (low red blood cell count). Definitive diagnosis is undertaken via additional blood testing. The total T4 (TT4) test is frequently used as a screening test. This test measures the amount of thyroid hormone that the thyroid gland is producing. When the TT4 is low, many veterinarians recommend either a free T4 test or a full thyroid profile to help confirm hypothyroidism. These tests are also used when the TT4 level is normal but your veterinarian still suspects hypothyroidism. Your veterinarian may also test for levels of other hormones (e.g., T3, thyroid stimulating hormone).

Once hypothyroidism is confirmed and treatment is started, the TT4 test will be used regularly to determine if the prescribed dose of medication provides enough hormone for your dog’s condition. Over time, the dosage of medication may need to be adjusted to meet the patient’s needs.

Affected Breeds

The Boxer, Chow Chow, Cocker Spaniel, Dachshund, Doberman Pinscher, Golden Retriever, Labrador Retriever, Poodle, and Giant Schnauzer are among the dog breeds that seem to be predisposed to the disease.


Synthetic thyroid hormone supplements are readily available to treat the condition.

This article has been reviewed by a Veterinarian.