Prolactin, also known as lactogenic hormone, luteotrophic hormone, and luteotrophin, is a peptide hormone synthesized and secreted by lactotrope cells in the anterior pituitary gland. It is also produced in other tissues including the breast and the decidua. Pituitary prolactin secretion is regulated by neuroendocrine neurons in the hypothalamus, most importantly by neurosecretory dopamine neurons of the arcuate nucleus, which inhibit prolactin secretion.

In mammals, prolactin stimulates the mammary glands to secrete milk and the corpus luteum of the ovary to secrete the hormone progesterone. Secretion of prolactin is increased by suckling. In birds prolactin stimulates secretion of crop milk by the crop glands.