The thyroid gland controls metabolism and many bodily functions. Disorders include hypothyroidism, causing fatigue, weight gain and cold sensitivity, and hyperthyroidism, causing weight loss, rapid heartbeat and anxiety. Autoimmune diseases like Hashimoto's and Graves' often cause these conditions; genetics, iodine levels, environmental exposures and some medicines also contribute. Diagnosis relies on blood tests; treatments range from hormone replacement to medications, radioactive iodine or surgery.
