Hypothyroidism in Cats

Hypothyroidism in cats occurs when the thyroid gland produces less thyroid hormone than the body needs. This hormone influences how cells use energy, so when levels drop, many processes in the body can slow down. In cats, this condition is uncommon and tends to appear in specific contexts—most often after treatment for an overactive thyroid, or occasionally as a primary gland problem. Owners may notice changes that develop gradually: reduced activity, weight gain without eating more, a dull or matted coat, or a cat that seeks warmth more than usual. Because thyroid hormone affects many systems, the signs can be subtle and easily attributed to other causes, particularly in older animals. Some cats show few outward changes and the condition is identified during investigation of something else. This page explores the patterns that may suggest low thyroid function, what is happening at a glandular and cellular level, how the condition is investigated through blood tests and clinical assessment, and the approaches available once a picture emerges. The aim is to help you understand what hypothyroidism in cats can look like and how it is typically approached.