TSH is a trophic hormone that stimulates the growth of thyroid follicular epithelial cells; therefore, levothyroxine sodium is often used to maintain the body’s TSH at a low level in patients with papillary, follicular, and Hürthle cell carcinomas. However, there is a lack of evidence as to which level of TSH is appropriate. In general, patients with residual cancer tissue or a high risk of recurrence need to maintain a TSH level below 0.1 mU/L, whereas in tumor-free patients with a low risk of recurrence, the TSH level can be mildly resistant or mildly above the lower limit of the reference value. For patients who remain tumor-free for many years, TSH values can be maintained within the reference range. Because TSH-suppressing levothyroxine sodium can cause some toxic effects on the body, such as tachyarrhythmias (especially in the elderly), bone decalcification (especially in postmenopausal women), and thyrotoxicosis-related manifestations. Therefore, the advantages and disadvantages of TSH suppression therapy need to be considered for each patient. For patients with long-term TSH suppression, a daily intake of calcium (1,200 mg/day) and vitamin D (1,000 U/day) is required.