If you are taking short-acting contraceptive pills: 1. it may cause irregular vaginal bleeding, which will be improved if you continue to take it. 2. because short-acting contraceptive pills are a combination of estrogen and progestin, it will lead to atrophy and thinning of the endometrium, and the effect on menstruation is to cause a decrease in menstrual flow. If you take the emergency contraceptive pill, because the emergency contraceptive pill can prevent ovulation of the ovaries, it will break the law of natural ovulation of the ovaries and cause endocrine disorders, which will be manifested as menstrual disorders, changes in menstrual cycle and changes in menstrual volume. Therefore, the above are the clinical effects of short-acting and emergency contraceptives on menstruation.