Which hormone primarily stimulates milk production during lactation?

• A. Estrogen
• B. Prolactin
• C. Oxytocin
• D. Testosterone

Answer: (B)

Milk production during lactation is driven mainly by prolactin, a hormone released from the anterior pituitary. Prolactin acts on the mammary alveolar cells to synthesize and secrete the components of milk, sustaining production after the baby is born. During pregnancy, estrogen and progesterone promote breast development but inhibit prolactin’s milk-producing action; after delivery, these hormones fall, allowing prolactin to stimulate milk synthesis. Oxytocin, on the other hand, triggers milk ejection (let-down) by contracting the myoepithelial cells around the ducts, not the production itself. Testosterone does not play a role in stimulating milk production.