The morning after pill is effective for up to 120 hours after sexual intercourse, However, its effectiveness decreases with time so it is important to act quickly. Evidence* indicates that levonorgestrel-based Emergency Hormonal Contraception will prevent 95% of expected pregnancies if taken within 24 hours of unprotected sex, 85% between 24-48 hours and 58% if used within 48-72 hours. *Task force on postovulatory methods of fertility regulation (1998). Randomised controllled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency. Lancet 352: 428-433