Adrenocorticotropic hormone (ACTH), a polypeptide hormone, consisting of 39 amino acids, which is synthesized from POMC (pre-opiomelanocortin) and secreted from corticotropes in the anterior lobe of the pituitary gland in response to the hormone corticotropin-releasing hormone (CRH) released by the hypothalamus. Adrenocorticotropic hormone* (also called ACTH or corticotropin) is secreted in short bursts every few hours and is increased by stress. In turn, ACTH controls secretion of corticosteroids, including cortisol (hydrocortisone), aldosterone, and androgens, by the adrenal glands. Most important of these is its stimulation of cortisol production.

ACTH production is partly controled by the hypothalamus and partly by the level of cortisol in the blood. When ACTH levels are high, the production of cortisol is increased; this, in turn, suppresses the release of ACTH from the pituitary. If ACTH levels are low, cortisol production falls and the hypothalamus releases factors that stimulate the pituitary to increase ACTH production.