The initial dose should be a low 25-50 μg per 24 hours, particularly in the case of severe myxoedema, cardiovascular disease and old age. Gradual increase every 4-6 week until maintenance dose. Too rapid an increase in the dose initially is a common cause of overdose symptoms. Usual maintenance dose is 100-150 μg per day, but varies from 50-300 μg per 24 hours.

Diagnosis and treatment of hypothyroidism must take place as soon as possible after birth to prevent mental retardation. The substitution need for thyroxine is greatest in infants but decreases as the child grows. Dosage per kg body weight decreases with age. The maintenance dose is usually 100-150 μg​/​m ² body surface. For newborns and infants with congenital hypothyroidism , where rapid substitution treatment is important, the recommended starting dose is 10-15 μg​/​kg body weight per 24/7 for the first 3 months. The daily dose must then be adjusted individually according to clinical findings and thyroid hormone and TSH values. For children who develop hypothyroidism , the recommended starting dose is 12.5-50 μg per day. 24 hours. The dose must be gradually increased every 2-4 days. week according to clinical findings and thyroid hormone and TSH values, until a maintenance dose is reached.