Subjects must discontinue HRT prior to study enrollment due to the potential for inhibition of Cytochrome P450 (CYP) enzymes that metabolize estrogens and progestins. For most forms of HRT, at least 2-4 weeks must elapse between the cessation of HRT and determination of menopausal status; length of this interval depends on the type and dosage of HRT. If a female subject is determined not to be post-menopausal, they must use adequate contraception, as defined immediately below.