Adrenocorticotropic hormone (ACTH or corticotropin) consists of 39 amino acids, the first 13 of which (counting from the N-terminus) may be cleaved to form α-melanocyte-stimulating hormone (α-MSH).  ACTH is a polypeptide hormone produced and secreted by the pituitary gland. ACTH acts through the stimulation of cell surface ACTH receptors, which are primarily located on the adrenocortical cells. ACTH stimulates the cortex of the adrenal gland and boosts the synthesis of corticosteroids, mainly glucocorticoids but also androgen steroids. ACTH is an important player in the hypothalamic-pituitary-adrenal axis.

ACTH synthesised from pro-opiomelanocortin (POMC) 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. It can be also produced by cells of immune system (T cells, B cells and macrophages) as a response to stimuli which go along with stress (including CRH).

POMC is cleaved into ACTH and β-lipotropin. γ-lipotropin and β-endorphin result from the cleavage of this β-lipotropin.  ACTH is also related to the circadian rhythm in many organisms. The half-life of ACTH in human blood is about 10 minutes.