Disparities in Emergency Contraceptive Metabolism Dictate Efficacy

The purpose of this study is to learn more about why some people are at greater risk for oral emergency contraceptive failure while others are not. The investigators want to learn if genetic differences impact the risk of emergency contraception failure.

Inclusion Criteria:Generally healthy womenAged 18-40regular menses (every 21-35 days) experiencing ovulatory cycles proven by a single progesterone level of 3 ng/mL or greater during the luteal phase of the screening cycle.Exclusion Criteria:Pregnant, seeking pregnancy, or breastfeedingKnown allergy to study medicationRecent use of hormonal contraceptionIrregular periods (<21 days or >35 day cycles)Routine use of nonsteroidal anti-inflammatory drugsMetabolic disordersSmokingAny condition that would preclude the provision of informed consentUsing drugs (within 2 weeks of study enrollment) known to interfere with the metabolism of UPA as well as drugs known to be CYP3A4 inducers, inhibitors, or CYP3A drug substrates