women 16 or older in UK(except Northern Ireland) sites, 17 years or more in Northern Ireland (UK) and 18 years or more in Ireland and US

present within 120 hours of unprotected intercourse

regular menstrual cycles

No current use of hormonal contraception

Willing to not use hormonal methods of contraception until study completion

At least one complete menstrual cycle (2 menses) post miscarriage, delivery or abortion

For women who present more than 72 hours after intercourse, decline the insertion of an Intra Uterine Device for emergency contraception

Able to provide informed consent

Willing to abstain from further acts of unprotected intercourse until study completion

Safety and Efficacy of CDB-2914 in Comparison to Levonorgestrel for Emergency Contraception