PIP: The hormonal aspects of lactation are discussed with reference to findings from animal studies. Both lactation and the specific stimulus of suckling are physiological phenomena involving hormones from both the anterior and the posterior lobes of the pituitary gland. In women and animals, complex hormonal changes occur during gestation, some contributing to development of mammary tissue enabling it to synthesize milk. Progesterone and estrogens are present in large amounts during pregnancy and reach peak levels near the end of pregnancy. Optimal breast development depends on other hormones also. Prolactin is the most important hormone for the actual initiation of lactation postpartum. It is, however, the fall in estrogen and progesterone levels once the fetus and placenta are delivered which gives the final stimulus to lactation. Suckling stimulates the nerve ends in the nipple area of the breast, causing increased milk production. Suckling and the presence of prolactin probably account for the reduced fertility observed during the lactation period. Emotional problems will interfere with the milk ejection reflex. Additionally, combination estrogen/progestin OCs (oral contraceptives) cause a reduction in the quantity of milk produced.