There are two main harmful effects of taking birth control pills during ovulation: first, it may cause abnormal uterine bleeding and irregular menstruation; second, there is still a possibility of unwanted pregnancy. Contraceptive pills generally refer to emergency contraceptive pills, emergency contraceptive pills are also a small amount of estrogen, a large number of progesterone drugs, can play the role of emergency contraception. It should be taken as soon as possible and no later than 48 hours after intercourse to prevent unwanted pregnancy, but it may cause menstrual disorders and endocrine disruption. In addition, the emergency contraceptive pill does not necessarily achieve a real contraceptive effect, is not safe and effective, if there is no recent childbearing requirements there are two ways to play an effective contraceptive, the first, the external condom, the second is recommended to oral short-acting contraceptive pills. Short-acting contraceptive pills are taken from the fifth day of menstruation, every night at bedtime to take 1 tablet, for 21 days, in 3-7 days after stopping the drug will be normal menstruation.