Glossary
Hypothyroidism
A condition in which the thyroid gland makes too little hormone, slowing the metabolism and causing weight gain, lethargy and coat and skin changes.
Also called: underactive thyroid, low thyroid, thyroid disease in dogs
The thyroid gland sets the pace of the body's metabolism. In hypothyroidism it produces too little hormone, usually because the immune system has attacked the gland. It is one of the more common hormone disorders in dogs and typically appears in middle age.
Signs build slowly. They include weight gain without eating more, tiredness, seeking warm places, a dull or thinning coat, flaky skin and repeated skin or ear infections. Breeds such as the Golden Retriever and Doberman Pinscher are often affected.
Because many of these signs are vague and can come from other illness, a vet needs blood tests to confirm it, and one low result is not always enough. Once confirmed, the condition is generally manageable with veterinary guidance. Do not give thyroid supplements bought for people.
Last reviewed November 8, 2026