Dexamethasone is a potent cortisol analogue (40 times greater than cortisol) which suppresses ACTH and cortisol production in normal individuals. After administration of a low dose of dexamethasone, a normal individual will show declines in ACTH and cortisol values, while a person with Cushing's disease or syndrome will not show suppression. This is primarily used to exclude Cushing's disease or syndrome (confirm normal). A failure to suppress is usually followed by additional testing such as a high dose dexamethasone or multiple low dose dexamethasone tests.

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