The medication can be started five days before the onset of menstruation and will ensure that menstruation does not occur during the continuous use of the medication, followed by withdrawal bleeding about three days after stopping the medication. Because medication is a hormonal drug, medroxyprogesterone acetate can change the physiological changes of the endometrium by regulating the progesterone level in women’s body. Since the change of progesterone can cause the endometrium to change from the proliferative phase to the secretory phase, it can regulate menstruation according to the change of progesterone level in the body. However, it should be noted that when using medroxyprogesterone acetate to regulate menstruation, the medication should be started five days before the onset of menstruation. If the medication is administered close to the menstrual period, it will be significantly more difficult to control the endometrium after it has already entered the secretory phase, which may result in failure to delay the menstruation.