The effect of taking birth control pills before menstruation depends on the type of pill. For short-acting contraceptives or long-acting contraceptives there is usually no significant effect, for emergency contraceptives the effect is usually greater. I. Short-acting contraceptive pills or long-acting contraceptive pills taken regularly generally do not have an obvious effect on the normal menstrual cycle, but may lead to a reduction in menstrual volume. For women with irregular menstrual cycles, regular use of short-acting contraceptives can be used to regulate the menstrual cycle; 2. Emergency contraceptives 1. increased menstrual volume: emergency contraceptives are highly effective progestins, which can lead to abnormal thickening of the endometrium and increase menstrual volume; 2. delayed or disrupted menstruation: taking emergency contraceptives can break the cyclical secretion of estrogen and progesterone by the ovaries, which may cause endocrine disruption and lead to menstruation 3. irregular vaginal bleeding: changes in the hormone level in women’s body may lead to exfoliative bleeding of the endometrium, usually irregular bleeding in the form of drops; 4. amenorrhea: excessive and frequent use of emergency contraceptives may lead to menstrual disorders or even amenorrhea. The side effects caused by contraceptive pills can generally recover on their own after 2-3 menstrual cycles, and if they do not return to normal for a long time, they need to regulate menstruation after checking the sex hormone six. In addition, when you have sex, you need to take reasonable contraceptive measures, and do not take the pill often to avoid affecting your health.