1. For the individual patient, the L-T4 dose of suppressive therapy is the dose required to achieve his or her TSH suppression goal. In patients with DTC who have cleared all of their thyroid, the L-T4 dose for suppression therapy is usually higher than the replacement dose alone, averaging about 1.5-2.5 μg/kg/d. In older patients (especially those over 80 years old), the L-T4 dose to achieve TSH suppression is 20%-30% lower than in younger patients because the reduced peripheral degradation rate of thyroid hormones in the elderly is greater than the reduced oral absorption rate. 2. The starting dose of L-T4 varies according to the patient’s age and concomitant disease conditions. 3. For example, for those whose thyroid gland has been completely cleared: the target dose is activated directly for young patients; for patients over 50 years old, if they have no heart disease and its tendency, the initial dose is 50μg/d; if the patient has coronary heart disease or other high-risk factors, the initial dose is 12.5-25μg/d or even less, with slower increments and longer adjustment intervals, and close monitoring of the heart condition. 4. The determination of the final dose of L-T4 depends on the monitoring of serum TSH. 5. During the L-T4 dose adjustment phase, TSH will be measured every 4 weeks or so, and thyroid function will be rechecked every 2-3 months for 1 year, every 3-6 months for 2 years, and every 6-12 months for 5 years after reaching the target to determine that TSH is maintained in the target range. 6, L-T4 taken on an empty stomach before breakfast is most beneficial for maintaining stable TSH levels. 7.If you miss a dose, you should take a double dose until all missed doses are made up. 8.Some patients need to adjust L-T4 dosage according to the change of TSH level in winter and summer (increase in winter and decrease in summer). 9.Some special drugs or foods should be taken after sufficient time interval: 1 hour interval with vitamins and tonic products; 2 hours interval with foods or drugs containing iron and calcium; 4 hours interval with milk and legumes; 12 hours interval with choleramide or lipid-lowering resin. 10. TSH can gradually reach steady state about 4 weeks after each adjustment of L-T4 dose (longer in older people). Do not stop the drug blindly during pregnancy.