Thyroid hormone replacement therapy treats underactive thyroid, a condition also known as hypothyroidism, according to WebMD. Patients generally receive synthetic thyroid hormone replacement with close monitoring to find the right dose of the drug for symptom relief.
Most hypothyroid patients start a course of levothyroxine, often sold under the brand names Synthroid or Levoxyl, notes WebMD. After taking the medicine for a period of six to eight weeks, the doctor checks the patient’s blood level to determine if the dose is appropriate and adjusts levels accordingly. Some patients require lifetime replacement therapy. However, if hypothyroidism stems from an infection or serious illness, thyroid levels may return to normal after recuperation, and medication is not necessary.