It is possible that taking birth control pills may cause a decrease in menstrual flow because they contain a large amount of hormones. Most emergency contraceptives contain progestin, which may lead to menstrual disorders, low menstrual flow or even amenorrhea, or prolonged periods, dripping menstrual blood, etc. It is not recommended to apply birth control pills for a long time, and you can choose other contraceptive measures, which have a small effect on menstruation and will be safer. During the contraceptive period, oral contraceptive pills, mood and emotional fluctuations, may also lead to low menstrual flow, do not be too anxious and nervous, pay attention to keep warm, etc., oral contraceptive pills may reduce the impact on menstruation. The decrease of menstrual flow is also related to the length of time of taking the pill, often the longer the application of the drug, the more obvious the decrease will be.