Ulipristal acetate (also known as CDB-2914 and PGL4001 and trade name Ella in the U.S) is a novel oral emergency contraceptive designed and developed by HRA Pharma. It is a selective progesterone receptor modulator, which reversibly blocks the progesterone receptors in target tissues it was approved in May 2009 by the European Commission and in August 2010 by the FDA as safe and effective in preventing unintended pregnancy for up to 120 hours – or five days – post- unprotected intercourse or contraceptive failure. Ella is not intended for routine use as a contraceptive. When taken immediately before ovulation is to occur, ella postpones follicular rupture. The likely primary mechanism of action of ulipristal acetate for emergency contraception is therefore inhibition or delay of ovulation; however, alterations to the endometrium that may affect implantation may also contribute to efficacy. The most common side effects are: headache, nausea, stomach (abdominal) pain, menstrual pain. Some women taking ella may have their next period earlier or later than expected. If your period is more than a week late, you should get a pregnancy test.