Levothyroxine sodium (L-T4) is the most effective medication for treating congenital hypothyroidism. The initial treatment dosage for newborns is 6~15 μg/kg/d, administered orally once daily, with the goal of normalizing elevated TSH levels within 2 weeks and achieving normal FT4 levels. Once serum FT4 and TSH are normal, follow-ups can be reduced to every 2-3 months, and after age 2, to every 3-6 months. Regular follow-up should monitor the patient's growth curve, IQ, bone age, and changes in serum FT4 and TSH.

Insufficient dosage of thyroid hormone can result in stunted growth and delayed skeletal development in children, while excessive dosage may lead to symptoms such as irritability, excessive sweating, weight loss, abdominal pain, and diarrhea.