A Study of Armour® Thyroid Compared to Synthetic T4 (Levothyroxine) in Previously Hypothyroid Participants

This study will include will include a Screening Period, double-blinded Titration Period (at least 18 weeks, up to 36 weeks), and a double-blinded Stabilization Period (12 weeks). Participants will be randomized to receive either their same dose of levothyroxine or an approximately, matching dose of Armour Thyroid, using a dose-conversion chart based on the United States Pharmacopeia (USP) Drug Information 2000, which states that 1 grain of Armour Thyroid is equivalent to 100 mcg of levothyroxine. During the Titration Period, Investigators will have the option to up-or down-titrate a participant's dose as needed based on the participant's TSH level (normal reference range 0.45 - 4.12 mIU/L, inclusive). At Week 18, if a participant's TSH levels are not within the normal reference range, the Investigator may up-or down-titrate the dose by continuing the Titration Period beyond Week 18 for up to a maximum of 3 additional titrations at 6-week intervals. Participants whose TSH levels have not normalized after the maximum 3 additional titrations will not enter the Stabilization Period. At the end of the Titration Period, participants with TSH levels within normal reference range may enter the Stabilization Period. Depending on whether a participant requires additional dose titration after the Week 18 visit, the Stabilization Period may end at Week 30, 36, 42, or 48.