The thyroid gland is the largest endocrine gland in the body and its main function is to synthesize thyroid hormones and regulate the body’s metabolism. Some thyroid diseases require surgical treatment. Whether to take Euthyrox (thyroxine) after surgery is determined by the extent of the surgically removed thyroid gland and the volume of the remaining thyroid gland as well as the recovery situation, so not all post-surgical thyroid surgery need to take thyroxine to maintain the treatment. The cases that require postoperative eugenol to prevent and control hypothyroidism are as follows: i. Since more than 2/3 of the thyroid gland has been surgically removed, the secretion of thyroxine is greatly reduced, and it must be maintained by oral thyroxine, or else hypothyroidism will occur; ii. Lifelong administration of eugenol is required after surgery for thyroid cancer, to replenish missing thyroxine on the one hand, and to inhibit the recurrence of thyroid malignant tumor recurrence.