There should be no menstrual flow during taking the pill. What happens when some patients get their periods twice a month while taking the pill? There are several situations: first, there may be problems with the drug itself, such as the expiration date of the drug or the quality of the drug; second, it may be that the endometrial condition was not evaluated before taking the pill, the endometrium should be in a thin state at the base to start taking the pill, if the endometrium itself is thick, after taking the pill there may be bleeding among Thirdly, there may be problems with the pill, such as differences in the amount of pills taken or missed pills, the most common of which may be missed pills or unstable pills, early and late, or irregular pills, which may cause bleeding, resulting in two periods a month.