Oral thyroid hormone is usually started (or continued) 24-72h after the treatment of thyroid purification, and the regular drug is L-T4. For those who have more thyroid tissues left before thyroid purification, because the 131I used for thyroid purification destroys the thyroid tissues so that the thyroid hormone will be released into the blood to varying degrees, the starting time of the L-T4 treatment can be appropriately delayed, and it is advisable to increase the dosage of L-T4 supplementation step by step.