Natural desiccated thyroid (NDT) is a doctor-prescribed thyroid drug that treats hypothyroidism -- an underactive thyroid gland. NDT includes natural forms of two key thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine). NDT drugs available in the United States include Armour® Thyroid, Nature-Throid®, WP Thyroid® and NP Thyroid®. Learn more about NDT now.