Used in the treatment of hypothyroidism, where the thyroid gland does not produce enough thyroid hormone. It serves as a synthetic replacement for natural thyroxine (T4), helping to restore normal hormone levels and regulate metabolism, energy, and overall growth and development. Commonly prescribed for patients who have undergone thyroidectomy or those with goiter and thyroid cancer. Also used in diagnostic procedures to suppress thyroid-stimulating hormone (TSH) for testing. The sodium salt form improves solubility and absorption in oral formulations.