Different birth control pills have different methods of administration and affect the body in different ways, so the timing of menstruation after taking them cannot be generalized. For the 21-pill combination short-acting contraceptive pill, menstruation usually occurs within 2-3 days after taking the 21-pill combination, but it may be delayed to about 1 week for some patients, but usually not more than 1 week. 28-pill combination short-acting contraceptive pill will cause menstruation while the patient is taking the pill, usually about 25 days after taking the pill, and it is not necessary to stop taking the pill during the whole menstrual period. The next cycle. The high hormone content of the emergency contraceptive pill can cause endocrine disruption and lead to menstrual disorders. However, it is important to exclude the possibility of unwanted pregnancy when taking emergency contraceptives with delayed periods. Oral contraceptive pills may have some side effects, such as gastrointestinal reactions, vaginal bleeding, etc. Serious cases should seek medical attention in time.