Take the contraceptive pill the second month of delayed menstruation is usually due to adverse drug reactions, contraceptive failure and other factors, common causes and treatment methods are as follows: 1, adverse drug reactions: contraceptive pills belong to hormonal drugs, if taken in the first half cycle of menstruation, will lead to excessive thickening of the endometrium, a period of time after taking the pill will appear withdrawal bleeding. After bleeding, the endometrium needs to be repaired, resulting in a delay in the next menstrual period. If taken in the second half of the menstrual cycle, it may cause prolongation of the luteal phase and delayed menstruation. This is more common and does not need to be treated, but can be observed. If the period is delayed for more than 1 week, you should go to the hospital in time, through ultrasound examination to make a clear diagnosis, you can apply progesterone to regulate the menstrual cycle under the guidance of the doctor; 2, contraceptive failure: the pill can not guarantee 100% contraception, if the period is delayed for more than 1 week, you can take the early pregnancy test or go to the hospital to test the blood HCG and other methods to determine whether pregnancy. After a woman is pregnant, because the body estrogen and progesterone levels rise sharply, inhibiting ovarian ovulation, resulting in the absence of menstruation; 3, other: the use of contraceptive pills to regulate menstruation, if the usual irregular menstruation, after taking the pill just regular menstruation that stop, it is likely to lead to irregular menstruation in the second month. In general, when using the pill to regulate menstruation, it is recommended to take the pill for three cycles before stopping it. In the treatment of polycystic ovary syndrome, if you stop taking the pill after only one cycle, it may lead to delayed menstruation. Therefore, for patients with polycystic ovary syndrome, if unmarried, it is recommended to alternate oral administration with progesterone to adjust the menstrual cycle. If you are married, especially if you have fertility requirements, you should take oral contraceptives to adjust the endocrine disorder and then perform ovulation treatment to restore the normal menstrual cycle.