Thyroid function and its regulation: The main function of the thyroid gland is the uptake and storage of iodine, synthesis and secretion of thyroxine. The main function of thyroxine is to regulate the material and energy metabolism of the body. Thyroxine accelerates the oxidation process of cells throughout the body, promotes the decomposition of proteins, lipids and carbohydrates, and increases the metabolic rate of the body. At the same time, it also plays an important role in promoting human growth and development, especially the growth and development of the skeleton and nervous system. The functional activity of the thyroid gland is regulated and controlled by the cortical-hypothalamus-pituitary system in a feedback manner. Thyroid stimulating hormone (TSH) secreted by the anterior pituitary gland directly excites the function of thyroid cells and promotes the secretion and synthesis of thyroxine. In addition to the feedback inhibition of thyroxine, TSH secretion is also stimulated directly by thyrotropin-releasing hormone (TRH) from the hypothalamus. When thyroxine release is increased, in addition to its inhibitory effect on pituitary TSH release, it also has an antagonistic effect on hypothalamic TRH release, indirectly inhibiting TSH secretion, thus forming a feedback regulatory system of the hypothalamus-pituitary-thyroid axis. In addition, the thyroid gland also has adaptive regulation of iodine deficiency or excess iodine in the body. For example, when the inorganic iodine content in the blood increases, it stimulates the thyroid gland to take up iodine and combine with tyrosine to produce more thyroxine, but when the inorganic iodine accumulation in the blood reaches a critical value, it can cause progressive inhibition of iodine and tyrosine binding and a decrease in thyroxine synthesis and release. The thyroid gland is controlled by these regulatory systems to maintain normal growth, development and metabolic functions. After total thyroidectomy for differentiated thyroid cancer, patients will be given oral thyroxine to compensate for the thyroid function and to inhibit the recurrence of thyroid cancer. Since the thyroid gland no longer exists, its pro-secretory effect on thyroxine will be lost regardless of the TSH level, and the concentration of thyroxine in the blood will directly depend on the dose of oral thyroxine. Therefore, generally speaking, doctors will choose an initial dose based on experience, such as 100ug of eugenol daily, but whether this dose is too much or too little is often unknown to both doctors and patients, and the way to determine this is to take blood for thyroid function measurement. The ideal situation is to have a normal thyroid function and a lower-than-normal TSH level to compensate for the thyroid function, prevent relapse, and not cause metabolic complications. It usually takes about 2 months to find this appropriate dose. The oral dose of Eugenol ranges from 100 to 150ug, such as 2.125 tablets (two tablets plus an eighth of a tablet) or 2.25 tablets (two tablets plus a quarter of a tablet) or 2.5 tablets, etc.