For the individual patient, the L-T4 dose of suppressive therapy is the dose required to achieve his or her TSH suppression goal. In differentiated thyroid cancer (DTC) patients with total thyroid clearance, the L-T4 dose for suppressive therapy is usually higher than the replacement dose alone, averaging about 1.5-2.5 μg/kg/d; in older patients (especially over 80 years of age), the L-T4 dose to achieve TSH suppression is 20%-30% lower than in younger patients, because the peripheral degradation rate of thyroid hormones is lower in older patients than the decrease in oral absorption rate. The starting dose of L-T4 varies depending on the patient’s age and concomitant disease. For example, in patients with a completely cleared thyroid gland, the target dose is started directly in younger patients; in patients over 50 years of age, the initial dose is 50 μg/d if there is no heart disease and no predisposition to it; in patients with coronary artery disease or other risk factors, the initial dose is 12.5-25 μg/d or less, with slower increments and longer adjustment intervals, and with close monitoring of cardiac status. During the L-T4 dose adjustment phase, TSH is measured every 4 weeks, and thyroid function is reviewed every 2-3 months for 1 year, every 3-6 months for 2 years, and every 6-12 months for 5 years to determine that TSH is maintained in the target range. Stable TSH levels are best maintained with a single dose of L-T4 on an empty stomach before breakfast. If a dose is missed, double the dose should be taken until the entire missed dose is made up. Some patients need to adjust the L-T4 dosage according to the changes in TSH levels in winter and summer (increase in winter and decrease in summer). Certain special medications or foods should be taken at sufficient intervals: 1 hour between vitamins and tonic products; 2 hours between foods or medications containing iron and calcium; 4 hours between milk and soy foods; 12 hours between bilirubin or lipid-lowering resins. TSH can gradually reach steady state about 4 weeks after each L-T4 dose adjustment (longer in elderly people). It is important not to stop the drug blindly during pregnancy.