Ulipristal acetate (UPA), a new entrant into the “morning after pill” market, has proven effective in preventing pregnancy when taken up to five days (120 hours) after sex.
UPA, marketed in Europe as ellaOne® since May 2009, blocks the progesterone hormone from creating proteins needed “to begin and maintain pregnancy.”
Traditional hormonal contraceptives have not involved progesterone, and some hope for further development with it.
UPA has been compared with levonorgestrel, which is used within three days of intercourse. Within 36 hours, UPA was more effective overall. It is worth noting that in this study UPA was less effective than levnorgestrel when taken the second day after intercourse.
UPA, taken between 97 and 120 hours of intercourse, was still effective in 98.32% of the intention-to-treat group. This group factors in the subjects who dropped out of the study for whatever reason.
In the modified-intention-to-treat group, which allows for dismissing study dropouts with enough justification, UPA worked in 75% of women who took the pill in the same time frame.
The drug is currently only available in Europe under prescription. Pending studies on its safety, it may become over the counter. The most common adverse side effects are headache and nausea.
In the United States, UPA is in the New Drug Application stage, the last stage before public availability.