After 5-6 weeks on the study medication, TSH levels will be checked and the medication adjusted to maintain TSH level between 0.46-4.68 mIU/L. Once the TSH level is in the desired range, subjects will continue the medication for an additional 6 weeks. Subjects will then be crossed-over to the other treatment arm for 3 months. Again, testing will be performed after each treatment period. Finally the subjects will again switched over to the 3rd arm and testing will be performed after treatment period.