Traditionally these hormonal medications are taken 72 to 120 hours after known or suspected barrier contraception failure or unprotected intercourse. The two standard steroidal EC methods are Plan BTM, containing of 0.75 mg levonorgestrel (LNG), and the Yuzpe method, containing 0.1 mg ethinyl estradiol (EE) and 0.5 mg LNG. Ovarian follicular development and ovulation in women have been studied after EC use; however, the mechanisms underlying follicular growth, regression, and ovulation during EC use remain poorly elucidated. The mechanism of action differs with each EC regimen as well as being dependent upon the relative timing between dosing, intercourse, and ovulation. Previous studies have shown that EC are most effective if used when the dominant follicle diameter is small (4 to 5 days prior to ovulation), however, during this time interval intercourse is less likely to result in pregnancy whether or not EC were administered.