Taking the emergency contraceptive pill may cause withdrawal bleeding, but it does not necessarily result in withdrawal bleeding. The main reasons for no withdrawal bleeding after taking the emergency contraceptive pill include: 1. the endometrium is not well proliferated when taking the emergency contraceptive pill, because the endometrium is very thin, and with the decline in the level of exogenous progesterone, no endometrial exfoliation occurs, so there is no withdrawal bleeding. 2. it may be that the contraceptive has failed, resulting in an unwanted pregnancy, and in this case, naturally, no withdrawal bleeding occurs. The specific cause cannot be determined based on clinical symptoms alone, and it is best to do a blood HCG laboratory test around day 7-10 after taking the emergency contraceptive pill to further clarify the diagnosis. If the emergency contraceptive pill is taken within 72 hours of unprotected sex, the effectiveness of contraception can reach 98%, the earlier the pill is taken, the better the effect of contraception, but taking the emergency contraceptive pill can only protect this sex.