Which infertility medication acts as a selective estrogen receptor modulator and induces ovulation, with estrogen agonist activity in some tissues and antagonist in others?

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

Answer: (B)

This question tests understanding of how selective estrogen receptor modulators (SERMs) work to induce ovulation. Clomiphene acts as a SERM, meaning it binds estrogen receptors but has different effects in different tissues. In the hypothalamus, it blocks estrogen negative feedback, which raises GnRH secretion and, in turn, increases FSH and LH from the pituitary to stimulate ovulation. In other tissues, it can behave as an estrogen antagonist or partial agonist, leading to tissue-specific effects such as changes in cervical mucus and endometrial receptivity. That combination—ovulation induction via hypothalamic disinhibition plus tissue-selective estrogen receptor activity—is what makes clomiphene the correct choice.

Why the others don’t fit: gonadotropins provide direct FSH/LH to the ovaries rather than modulating estrogen receptors; letrozole lowers estrogen production through aromatase inhibition to boost gonadotropin release indirectly (not a SERM); metformin works mainly as an insulin sensitizer and does not act on estrogen receptors to induce ovulation.