The so-called 21-pill contraceptive pill is actually a short-acting contraceptive pill, which is mainly composed of estrogen and progesterone. After taking short-acting contraceptive pills, women will directly affect the endocrine and ovulation functions of the ovaries due to the supplemental secretion of estrogen and progesterone in the body, thus achieving contraception. Generally, it is necessary to start taking the pill during menstruation, mostly within the 2nd-5th day of menstruation, and it takes 7 consecutive days before the pill can take effect to produce a contraceptive effect. If intercourse is arranged too early, other contraceptive measures are still needed. Moreover, during the whole period of taking the pill, there should not be any omission of taking the pill, and it is better to take the pill at the same time period according to the course of treatment, so as to avoid causing irregular vaginal bleeding.