RecruitingDrug trialA Study to Assess the Safety and Efficacy of Oral Armour Thyroid Compared to Synthetic T4 for the Treatment of Primary Hypothyroidism in Adult ParticipantsThis study will evaluate the efficacy and safety of Armour Thyroid treatment compared with synthetic T4 in subjects who have primary hypothyroidism and are currently stabilized (i.e., in-range thyroid-stimulating hormone \[TSH\]) on synthetic T4 treatment. This study will also therefore evaluate the efficacy and safety of dose conversion from synthetic T4 therapy to Armour Thyroid therapy.