Prolactin is a hormone produced from the pituitary gland. It helps stimulate and maintain breast milk production. Hyperprolactinemia describes an excess of this hormone in a person’s body. It’s normal to have this condition during pregnancy or when producing milk for breastfeeding. Certain conditions or use of specific medications, however, can cause hyperprolactinemia in anyone. The causes and effects of high prolactin levels vary depending on a person’s sex.