Mifepristone + Misoprostol (Medical Abortion / Induction)

Mifepristone + misoprostol is the standard two-drug regimen for medical abortion and cervical ripening/labor induction, and USMLE Step 1 tests this primarily at the mechanism level. The key conceptual point is that these two drugs work sequentially through completely different mechanisms — mifepristone primes the uterus by blocking progesterone, and misoprostol then triggers the contractions. It's a low-yield topic, but when it shows up, it's almost always testing whether you confuse mifepristone's antiprogestational action with a direct uterotonic effect.

The tricky part is that students often mentally lump all 'abortion drugs' into a single category of 'something that causes contractions.' Mifepristone does not cause contractions — it's a competitive progesterone receptor antagonist (RU-486) that starves the decidua of progesterone support, causing endometrial breakdown and cervical softening. Only after this priming step does misoprostol come in as a prostaglandin E1 analog to drive cervical ripening and uterine contractions to expel the embryo. If you reverse the roles or conflate the mechanisms, you'll miss the question.

On USMLE Step 1, this is unlikely to appear as a standalone recall question. More likely you'll see it embedded in a pharmacology passage asking you to identify which drug class a described mechanism belongs to, or asking what happens if you give misoprostol without mifepristone (the decidua still has progesterone support — much less effective). Know misoprostol's class (PGE1 analog, not oxytocin) cold, because misoprostol also appears in GI contexts (peptic ulcer disease), and the exam loves cross-context drug recognition.