Prolactin is a hormone that is primarily involved in milk production and breast development. After you have a baby, your prolactin levels rise and cause your mammary glands to lactate, so you can breastfeed. Hyperprolactinemia is a condition characterized by high prolactin levels not related to pregnancy. If you have high prolactin levels in your body and you are female, your main symptom will probably be related to your menstrual cycle. Most women with hyperprolactinemia have some disruption to their cycles. This may show up as irregular periods, abnormal flow or loss of menstruation altogether (amenorrhea).