Prolactin is a hormone which main target organ is the mammary gland. Prolactin is necessary for the development and production of maternal milk (lactation) after childbirth. Prolactin production is carried out in the pituitary gland (brain gland) and is stimulated by many factors, including receptors located in the nipple areola. When a newborn is placed to the mother's breast, these receptors are irritated, an impulse is sent to the brain which leads to prolactin production and, as a result, mother's milk production. Another hormone, oxytocin, is responsible for removing milk from the breast.

There are about 300 known functions of prolactin (“Prolactin and its receptors” by S. Bolle-Feissot, W. Goffin, 1998)

During pregnancy, the concentration of prolactin increases, but lactation does not occur due to the presence of progesterone in blood. Progesterone is produced in large quantities by the placenta, and after delivery it leaves the body. The concentration of progesterone begins to decrease “unlocking” the prolactin activity.

High levels of prolactin in blood result that the woman cannot get pregnant, which happens both with pathology and under the normal condition (physiological lactational amenorrhea after childbirth). The fact is that prolactin reduces the production of FSH. It is the hormone responsible for the maturation of the ovum.

Prolactin is responsible for sexual satisfaction after sexual intercourse. Excessively high levels of prolactin contribute to a decrease in estrogen in women and testosterone in men, which causes a decrease in libido and leads to impotence.