Prolactin is the primary hormone responsible for stimulating milk production (lactogenesis) in the mammary glands of lactating women. It acts on the alveolar cells of the breast to promote synthesis and secretion of milk. While oxytocin triggers milk ejection by causing myoepithelial cell contraction, it does not influence milk synthesis. Estrogen and progesterone support breast development during pregnancy but inhibit prolactin’s effect on milk production until after delivery. Hence, prolactin is essential for initiating and maintaining lactation post-partum.

Reference: Ganong’s Review of Medical Physiology, Barrett KN, 26th Edition.