Hormone produced by the thyroid glands to regulate metabolism by controlling the rate of oxidation in cells. Cases of hypothyroidism, where the gland is insufficiently active, can be treated by administration of thyroxine or a combination of thyroxine and triiodothyronine. L-Thyroxine (T4) and triiodo-L-thyronine (T3) are iodine-containing hormones produced from thyroglobulin in the thyroid follicular cells. The stimulation of metabolic rate and regulation of growth and development by these