Irregular menstruation after taking birth control pills may be related to the fluctuation of sex hormone levels in the body caused by birth control pills. Contraceptive pills usually contain estrogen or progesterone, estrogen and progesterone will cause some changes in the level of sex hormones in the body, and the changes in sex hormones will stimulate the uterine lining to cause menstrual irregularities such as excessive or insufficient menstruation, early or delayed menstruation, and prolonged or irregular menstruation. If you have irregular periods after taking birth control pills, you can stop taking the pills for observation. Short-acting birth control pills need to be used for one cycle before stopping the pills, and usually within one or two months after stopping the pills, your body will be able to adjust itself to resume normal menstruation. If menstruation is still not normal after stopping the pill, you need to go to the hospital for examination and medication to regulate menstruation.