Hello..... I pills are progesterone pills. Levonorgestrel emergency contraceptive pills prevent pregnancy by preventing or delaying ovulation. They may also work to prevent fertilization of an egg by affecting the cervical mucus or the ability of sperm to bind to the egg. ,it is taken within 72 hours of sexual intercourse . it only prevent implantation of ovulation . it may alter period a week here and there.have a 5%-20% failure rate. .If you miss regular menses do urine pregnancy test ,if it comes positive consult gynecologist