The primary care provider determines that Ms. A has hypothyroidism and orders a pregnancy test for her because she cannot recall the time of her last menstrual period. Ms. A wants to know why this is so important. She states, “I know I’m not pregnant. I have been very careful since the birth of my son.” What is your most appropriate response? What medication interactions, if any, would you anticipate in this case with initiation of thyroid hormone replacement therapy?