Which hormone promotes lactation in postpartum women?

Prolactin is the hormone primarily responsible for promoting lactation in postpartum women. It is produced by the anterior pituitary gland and plays a crucial role in the development of mammary glands and the initiation of milk production following childbirth. The levels of prolactin increase during pregnancy, preparing the breasts for milk production, and its secretion continues to be stimulated by suckling, which helps maintain milk supply for breastfeeding.

In contrast, estrogen and progesterone are important hormones during pregnancy that prepare the body for lactation, but they inhibit lactation until after delivery. Postpartum, the levels of these hormones drop significantly, allowing prolactin to take effect without inhibition. Oxytocin, while it does play a role in the breastfeeding process by promoting milk ejection (the "let-down" reflex), is not the primary hormone responsible for the production of milk itself. Therefore, the key hormone that stimulates lactation after childbirth is prolactin.