This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The specific aim of this study is to determine whether there is a significant difference in thyroid stimulating hormone levels between two different preparations of levothyroxine that are declared therapeutically equivalent by the FDA.