Taking birth control pills may cause a decrease in menstrual flow. If it is a long-acting birth control pill, it has little effect on menstruation during the period of taking the pill. If you stop taking the long-acting contraceptive pill, it may affect your menstruation, resulting in decreased menstrual flow, at which time you need to use a short-acting contraceptive pill to regulate your menstrual flow. Short-acting birth control pills have a very small effect on menstruation and have the effect of regulating menstruation. For irregular menstruation caused by abnormal ovarian function, it can be regulated by taking short-acting birth control pills. If you are taking emergency contraceptive pills, it will have an effect on the menstrual cycle, which may cause early menstruation or delayed menstruation or a decrease in the amount of menstruation. Emergency contraceptive pills may also cause amenorrhea if taken several times in a short period of time. If you want to take contraceptive measures, taking short-acting contraceptive pills has fewer side effects and is more effective.