Clinical Research Details Clinical Research Hypothyroidism: Efficacy and Safety of Armour Thyroid Treatment in Subjects with Primary Hypothyroidism Study Description The purpose of this study is to evaluate if Armour Thyroid is safe and effective in the treatment of hypothyroidism. This study will compare the effect of Armour Thyroid on hypothyroidism and its safety with synthetic drug T4 (Levothyroxine). The number of FDA-approved and commercially available options for the treatment of hypothyroidism are limited. Currently, synthetic T4 is the common thyroid replacement therapy. Prior to the mid-1970s, desiccated thyroid, such as Armour Thyroid, was the most commonly prescribed form of thyroid hormone replacement. Some of the patients treated with synthetic T4 continue to have persistent symptoms of hypothyroidism or inadequate improvement of their hypothyroid symptoms. The use of desiccated thyroid (Armour Thyroid) may be beneficial to patients with hypothyroidism. Inclusion/Exclusion Criteria Inclusion: Age 18-15, inclusive, Diagnosis of primary hypothyroidism, Be on continuous thyroid replacement therapy of synthetic T4 for primary hypothyroidism, Be on a stable FDA approved daily dose of synthetic T4 Open Enrollment Contact Name: Renae BurrContact Phone: (904) 244-0986Contact Email: renae.burr@jax.ufl.edu Investigators Joe M. Chehade, M.D. Medicine Christian A. Koch, M.D., Ph.D., FACP, MACE Medicine Payal P. Shooliz, M.D. Medicine