[2] Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary gland to suppress the secretion of adrenocorticotropic hormone (ACTH).

Specifically, dexamethasone binds to glucocorticoid receptors in the anterior pituitary gland, which lie outside the blood–brain barrier, resulting in regulatory modulation.

[citation needed] A normal result is a decrease in cortisol levels upon administration of low-dose dexamethasone.

If the cortisol levels are unchanged by low- and high-dose dexamethasone, then other causes of Cushing's syndrome must be considered with further work-up necessary.

[6] †ACTH as measured prior to dosing of dexamethasone[7] Equivocal results should be followed by a corticotropin-releasing hormone stimulation test, with inferior petrosal sinus sampling.