Which drug is known to cause an LH surge when used for ovulation induction?

• A. Letrozole
• B. Clomiphene
• C. Misoprostol
• D. Gonadotropins

Answer: (B)

Ovulation induction works by nudging the hypothalamic-pituitary axis to produce a mid‑cycle LH surge that triggers ovulation. Clomiphene citrate acts as a selective estrogen receptor modulator that binds estrogen receptors in the hypothalamus, blocking estrogen’s negative feedback. This increases GnRH pulse frequency from the hypothalamus, which raises pituitary LH (and FSH) secretion. The resulting LH surge is the key signal that prompts ovulation of the matured follicle.

Letrozole lowers estrogen production by inhibiting aromatase, which also reduces negative feedback and raises FSH, promoting follicular growth, but the rise in LH is not the defining feature of its action. Misoprostol is unrelated to inducing ovulation. Gonadotropins deliver FSH (and sometimes LH) directly to the ovary and require additional steps to trigger ovulation, so the characteristic, reliably described LH surge from the hypothalamic-pituitary axis is most classically associated with clomiphene.