It is because it is a contraceptive pill that contains estrogen and progestin. The mechanism of contraception is to inhibit ovulation in women, and the drug accumulates in the body until a few days before it can take effect. In addition, this drug is taken on the first day of menstruation, when the follicles in the woman’s body have not yet begun to develop, so the effect will be felt after 7 days of taking the pill. Take this pill for contraception must be careful, it is best to take it at a fixed time every day to be able to keep the hormone levels in the blood in a stable state. You must not forget to take the pill, forgetting to take it will not only affect the effectiveness of contraception, but also lead to vaginal bleeding.