Thyroid glandulars are very similar to Natural Desiccated Thyroid formulations with a few notable differences: The first is that NDT formulations like Armour Thyroid and NP Thyroid contain standardized amounts of T4 and T3 in each unit of measurement or grain. Given their source, thyroid glandulars also likely contain some amount of T4, T3, T2, and T1, but their dose is unknown and likely changes from lot to lot. Another big difference is their availability. Armour Thyroid and NP Thyroid are available only as prescriptions and require a doctor to obtain them. Thyroid glandulars are available over the counter and can be purchased by anyone. It's for these reasons that many thyroid patients opt to take glandulars.