On January 29, 2010 The Lancet published the results of a study which compared levonorgestrel (LNG) to ulipristal acetate, a selective progesterone-receptor modulator. Ulipristal caused a greater reduction in pregnancies when ingested within 72 hours of intercourse compared to LNG, as well as when ingested 73-120 hours. As the researchers noted: "... ulipristal acetate almost halved the risk of becoming pregnant compared with levonorgestrel..." (1)

Ulipristal is reported to have a mechanism of action that bears a "striking similarity" to the mechanism of action of mifepristone (RU-486). (2) The researchers stated that the dose of ulipristal was formulated to inhibit ovulation and the dose might be too low to inhibit implantation, "although an endometrial effect ...cannot be excluded."

Based upon the preceding evidence, ulipristal is an abortifacient drug. Further conclusions must await future research.

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(1) Glasier AF, Cameron ST, Fine PM et al, op.cit.

(2) Benagiano G, von Hertzen Helen. Towards more effective emergency contraception? Lancet.2010;375:527-528