<prompt> Progesterone of choice in emergency contraception is?NorethisteroneMedroxyprogesteroneOxytocinLevonorgestrel  <response>: Unprotected intercourse without regard to the time of the month carries an 8 incidence of pregnancy, an incidence that can be reduced to 2 by the use of emergency contraceptives within 72 hours of unprotected intercourse. 0.75 mg levonorgestrel are now approved for postcoital contraception and are available over the counter for women aged 17 years. Levonorgestrel is more effective and is associated with fewer side effects than the combination estrogen-progestin regimens. Basically the methods used interfere with the physiological events before implantation, for e.g. inhibition or delaying of ovulation or interference with postovulatory events necessary for implantation longevity of the blastocyst. REF : gynecology book of shaw 17th 