Ulipristal acetate, a progesterone receptor modulator for emergency contraception.

Unwanted pregnancy is a global reproductive health problem. Emergency contraception is defined as the use of drug or device after unprotected or underprotected intercourse to prevent an unwanted pregnancy. 1.5 mg of levonorgestrel as a single dose or in two doses with 12 h apart taken within 72 h of unprotected intercourse is the current gold standard emergency contraception regimen. This method is only effective if used as soon as possible after sexual intercourse and before ovulation. A single dose of 30 mg ulipristal acetate, a novel selective progesterone receptor modulator, has recently been proposed for the emergency contraception use up to 120 h of unprotected intercourse with similar side effect profiles as levonorgestrel. Ulipristal acetate could possibly prevent pregnancy when administered in the advanced follicular phase, even if luteinizing hormone levels have already begun to rise, a time when levonorgestrel is no longer effective in inhibiting ovulation.