A 24-year-old woman presents to the emergency department 18 hours after unprotected intercourse. She is requesting emergency contraception. Which of the following is the most effective emergency contraceptive agent when used within 72 hours of unprotected intercourse?

Explanation

## Emergency Contraception: Efficacy Comparison **Ulipristal acetate (30 mg single dose)** is the most effective emergency contraceptive agent available, with efficacy remaining high even up to 120 hours (5 days) after unprotected intercourse. ### Comparative Efficacy: | Agent | Timing | Efficacy | Mechanism | |-------|--------|----------|----------| | **Levonorgestrel** | ≤72 hours | 60–90% | Progestin; delays/inhibits ovulation | | **Ulipristal acetate** | ≤120 hours | >95% | Selective progesterone receptor modulator; more effective if given closer to ovulation | | **Mifepristone** | ≤72 hours | ~85% | Progesterone antagonist; delays ovulation | | **Copper IUD** | ≤5 days | >99% | Spermicidal/inflammatory; most effective but invasive | **Key Point:** Ulipristal acetate is a **selective progesterone receptor modulator (SPRM)** that is significantly more effective than levonorgestrel, particularly in the luteal phase when levonorgestrel efficacy drops. It is WHO-recommended as the first-line pharmacological emergency contraceptive. **High-Yield:** Among oral agents, ulipristal acetate > mifepristone > levonorgestrel in efficacy. The copper IUD is most effective overall but requires insertion. **Clinical Pearl:** In this case, the patient is at 18 hours post-intercourse, well within the window for ulipristal acetate, making it the optimal choice.