ellaOne is a medicine that contains ulipristal acetate, which acts as a selective progesterone receptor modulator. The mechanism of the emergency contraceptive pills is not fully known, however their effect is thought to result from the preventing ovulation and endometrium growth. In a regular menstrual cycle the maturing egg eases toward the surface of the ovary, and the increased production of progesterone stops other eggs from being released. Ulipristal acetate sends a signal that ovulation has already taken place, and therefore no egg is released to the ovary. Additionally, the synthetic hormone thickens the cervical mucus, which makes it harder for the sperm to get through the cervix in order to fertilize the egg.
As the implementation and fertilization process takes as long as five days, there is a high ellaOne pregnancy prevention rate.
Note that the rate decreases, however, with each passing day, therefore the pill should be taken as soon as possible to be effective.
According to the statistics only 2 women out of 100 got pregnant after using the ellaOne emergency contraceptive pill within the 5 days from having intercourse.