Hormonal methods for emergency contraception.

The World Health Organization includes oral emergency contraception (EC) in the list of essential medicines. Ulipristal acetate (UPA) and levonorgestrel (LNG) are the recommended oral methods. UPA has superior efficacy and a comparable side effect profile compared with LNG. Both work by inhibiting or delaying ovulation, so that sperm present in the reproductive tract will have lost their fertilising ability by the time the oocyte is eventually released. Neither LNG nor UPA at the EC doses have significant effects on the endometrium and are unable to prevent implantation. Mifepristone can also be used for EC but its availability is limited to few countries. LNG is less effective in women with a body mass index over 26 kg/m2 or weight over 70 kg. Hormonal contraception can be quickstarted immediately following LNG, or five days following UPA. LNG-releasing intrauterine devices and cyclo-oxygenase inhibitors are promising options for EC to be further studied.