Morning-after pills can help prevent pregnancy if you've had unprotected sex — whether you didn't use birth control, you missed a birth control pill, you were sexually assaulted or your method of birth control failed.

Morning-after pills do not end a pregnancy that has implanted. Depending on where you are in your menstrual cycle, morning-after pills may act by one or more of the following actions: delaying or preventing ovulation, blocking fertilization, or keeping a fertilized egg from implanting in the uterus. However, recent evidence strongly suggests that levonorgestrel doesn't keep a fertilized egg from implanting. It's not clear if the same is true for ella.

Keep in mind that the morning-after pill isn't the same as mifepristone (Mifeprex), also known as RU-486 or the abortion pill. This drug terminates an established pregnancy — one in which the fertilized egg has attached to the uterine wall and has already begun to develop.

April 14, 2015