Which statement correctly describes Metyrapone?

• A. It blocks cortisol synthesis and increases ACTH
• B. It decreases ACTH
• C. It substitutes cortisol and decreases ACTH
• D. It increases cortisol production

Answer: (A)

Metyrapone blocks the enzyme 11β-hydroxylase, the step that converts 11-deoxycortisol to cortisol in the adrenal cortex. When this step is inhibited, cortisol production drops. The pituitary senses the fall and responds by increasing ACTH release to stimulate the adrenal gland. This rise in ACTH, along with accumulation of cortisol precursors like 11-deoxycortisol, is the hallmark of metyrapone’s action and why it’s used to test the integrity of the hypothalamic-pituitary-adrenal axis. So, describing it as blocking cortisol synthesis and increasing ACTH best fits its pharmacologic effect and physiologic response.