Determining the Impact of Combined Hormonal Contraceptives on Ulipristal Acetate

Emergency contraception (EC) provides women with an additional line of defense against unintended pregnancy during an act of unprotected intercourse. An antiprogestin, ulipristal acetate (UPA; ellaTM), has emerged as one of the most effective oral options. However, there is currently a lack of information regarding the practical use of UPA. Basic science studies have shown that UPA binds to and prevents progesterone receptor from working, leading to the possible concern that hormonal contraceptives, like the birth control pill, would prevent UPA from working. Ideally, women should start their regular method of birth control soon after EC use but by doing this, they may prevent the UPA EC from working. A woman could just delay starting her regular method of birth control but then she is still at risk for pregnancy.

This proposal has been designed to address this gap in knowledge and will focus on the impact of the birth control pill on UPA's ability to delay ovulation (or the release of an egg). Subjects will undergo a referent cycle UPA only (Cycle 1, 1 month), followed by a washout cycle (Cycle 2, 1 month) and finally UPA with combined oral contraceptives (COCs) dosed 2 days later (Cycle 3, 1 month treatment cycle). The hypothesis is that starting the birth control pill shortly after UPA adversely impacts UPA's ability to delay ovulation.