Which of the following is true regarding RU 486?
**Core Concept**
RU 486, also known as mifepristone, is a potent antiprogestin medication used in medical abortion and as an emergency contraceptive. It works by competitively inhibiting the action of progesterone at the progesterone receptor, thereby disrupting the early stages of pregnancy.
**Why the Correct Answer is Right**
Mifepristone binds to the progesterone receptor, preventing progesterone from binding and exerting its effects on the endometrium and embryonic development. This leads to decidualization and detachment of the endometrium, which ultimately results in the termination of pregnancy. The mechanism of action of mifepristone is critical in understanding its use as an abortifacient and emergency contraceptive.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because RU 486 does not primarily act as an estrogen receptor antagonist.
**Option B:** This option is incorrect because RU 486 is not primarily used as a treatment for endometriosis.
**Option C:** This option is incorrect because RU 486 does not primarily act as a GnRH agonist.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that mifepristone is a potent antiprogestin and should be used under close medical supervision to avoid potential complications. Additionally, mifepristone can have significant interactions with other medications, including corticosteroids and certain anticoagulants.
**Correct Answer: C. RU 486 is an antiprogestin medication used in medical abortion and as an emergency contraceptive.**