The thyroid gland controls how quickly the body uses energy, makes proteins, and controls the body's sensitivity to other hormones. It participates in these processes by producing thyroid hormones, the principal ones being thyroxine (T 4) and triiodothyronine (T 3), which is more active.These hormones regulate the growth and rate of function of many other systems in the body. T 3 and T 4 are synthesized from iodine and tyrosine.yperthyroidism occurs when the gland produces excessive amounts of thyroid hormones, the most common cause being Graves' disease —an autoimmune disorder. In contrast, hypothyroidism is a state of insufficient thyroid hormone production. Worldwide, the most common cause is iodine deficiency.