Emergency contraceptive drug Paustin contains certain estrogen and progesterone, which can inhibit ovulation and can change the properties of cervical mucus, which can increase the consistency of cervical mucus and facilitate the penetration of spermatozoa. It can also change the morphology and function of the endometrium, which is not conducive to embryo implantation. It can also change the function of the fallopian tubes, because the epithelial cilia function of the fallopian tubes under the action of estrogen and progesterone may affect the implantation of the fertilized egg to achieve the effect of contraception. Normal birth control pills have about 80% effectiveness, regardless of the brand, even if it is Paustin, there will be a 20% chance of failure. So after taking oral emergency contraceptives, check 12 days after intercourse to rule out pregnancy as it is not 100% contraceptive.