Prolactin (PRL), also known as luteotropin or luteotropic hormone, is an endogenous peptide hormone produced primarily by the anterior pituitary gland. It belongs to the protein hormone class and is encoded by the PRL gene in humans. Prolactin is synthesized and secreted by lactotroph cells in the pituitary and plays a crucial role in various physiological processes. Researchers have extensively studied prolactin for its involvement in lactation, reproductive functions, and its broader role in homeostasis. The primary physiological roles of prolactin include the stimulation of milk production in mammals, regulation of the immune system, and modulation of reproductive behaviors. Research areas have expanded to include its effects on metabolism, osmoregulation, and its potential role in certain pathologies such as prolactinomas and hyperprolactinemia. Prolactin exerts its effects through binding to the prolactin receptor, a member of the cytokine receptor superfamily. This interaction activates the JAK2-STAT signaling pathway, leading to the transcription of target genes involved in milk production and other physiological processes. Researchers have found that prolactin's mechanism of action is complex, involving cross-talk with other hormonal pathways. The pharmacokinetic properties of prolactin indicate a circulating half-life of approximately 15-20 minutes. It is primarily metabolized in the liver and kidneys, with its bioavailability being largely dependent on endogenous secretion rather than exogenous administration. Clinical use of prolactin is limited, as it is not typically administered as a therapeutic agent. However, its levels are measured in clinical settings to diagnose and manage conditions like prolactinomas and infertility. Regulatory standing for prolactin as a therapeutic agent is not applicable, as it is not used in pharmacological treatments.