The purpose of this study is to assess the safety and efficacy of CDB-2914 in comparison to levonorgestrel for preventing pregnancy up to 5 days after unprotected sexual intercourse.

Inclusion Criteria:

• 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

Exclusion Criteria:

• One or more acts of unprotected intercourse more than 120 hours
• current or recent use of hormonal methods of contraception
• currently pregnant or breastfeeding
• tubal ligation or current use of IUD
• Use of hormonal emergency contraception since last menstrual period
• Current use of IUD
• Tubal ligation
• Partner with a vasectomy
• Unsure about the date of the last menstrual period
• Severe asthma insufficiently controlled by oral glucocorticoid
• Hypersensitivity to the active substance levonorgestrel or any of the excipients of the drug products used in the study