This question examines hypothyroidism. L- thyroxine generally starts from 25 ~ 50μ g/d and increases by 25μg every 1 ~ 2 weeks until the therapeutic goal is achieved. Patients with no previous history of heart disease can reach the complete replacement dose as soon as possible. Patients with ischemic heart disease should start with a small dose and slowly adjust the dose. The half-life of L-T4 is 7 days, and it is enough to take/kloc-0 once a day. In general, the replacement dose of adult patients is 50 ~ 200μ g/d. Food, calcium and cholic acid chelating agent (cholestyramine) will affect the absorption of L-T4. The best time to take medicine is 1h before breakfast, followed by bedtime and 30 minutes before breakfast. Patients with hypothyroidism need to take medicine for life.