Triiodothyronine hormone molecule. Computer model showing the structure of the hormone triiodothyronine (T3). Atoms are colour-coded (carbon: dark grey, hydrogen: light grey, oxygen: red, nitrogen: blue, and iodine: purple). Triiodothyronine is produced by the follicular cells of the thyroid gland. It is the most powerful thyroid hormone and affects almost every process in the body, including body temperature, growth, and heart rate.