EllaOne is known as a 'morning after pill'. It is used to reduce the chances of becoming pregnant after unprotected sex or failure of a contraceptive method.
EllaOne tablets contain the active ingredient ulipristal acetate, which is a type of medicine called a selective progesterone receptor modulator. It works by acting on the body's receptors for the naturally occurring female sex hormone, progesterone.
It is not fully understood how this medicine prevents pregnancy. It is thought to work by preventing ovulation and fertilisation and also by altering the lining of the womb, depending on which stage of the menstrual cycle the woman is at.
In a woman's normal menstrual cycle, an egg matures and is released from the ovaries (ovulation). The ovary then produces progesterone, which prevents the release of further eggs. Ulipristal tricks the body processes into thinking that ovulation has already occurred. This prevents the release of eggs from the ovaries.
Ulipristal also increases the thickness of the natural mucus at the neck of the womb (cervix), making it more difficult for sperm to cross from the vagina into the womb. By preventing sperm entering the womb, successful fertilisation of any egg that is there is less likely.
Ulipristal is also thought to alter the lining of the womb, preventing it from being prepared for a fertilised egg. This means that if an egg is released from the ovaries and is fertilised, it cannot implant into the womb and therefore pregnancy is avoided.
The whole process from fertilisation to implantation in the womb can take up to five days, so EllaOne can only stop pregnancy from occurring for up to 120 hours after unprotected sex. However the sooner it is taken after unprotected sex, the more effective it will be.