Hyperprolactinemia is a condition of too much prolactin in the blood of women who are not pregnant and in men. Hyperprolactinemia is relatively common in women. About a third of women in their childbearing years with irregular periods but normal ovaries have hyperprolactinemia. When this happens, a woman might have trouble getting pregnant or her breasts may start producing milk outside of pregnancy (galactorrhea). Ninety percent of women with galactorrhea also have hyperprolactinemia. High prolactin levels interfere with the normal production of other hormones, such as estrogen and progesterone. This can change or stop ovulation (the release of an egg from the ovary). It can also lead to irregular or missed periods. Some women have high prolactin levels without any symptoms.