Prolactin is a hormone occassionally overproduced by the brain, interfering with normal reproductive function.

Prolactin is a hormone secreted by the pituitary gland (located at the base of the brain). Normally, prolactin is present in the blood stream in low levels in nonpregnant women. During pregnancy, prolactin levels increase approximately ten-fold and stimulate milk formation. Hyperprolactinemia is a condition where the brain secretes too much prolactin in a woman who is not pregnant. Hyperprolactinemia can produce a variety of reproductive dysfunctions including inadequate progesterone production during the luteal phase after ovulation, irregular ovulation and menstruation, absence of menstruation, and galactorrhea (breast milk production by a woman who is not nursing).

Prolactin levels should be measured in women who experience these conditions. Prolactin secretion may increase mildly with sleep, stress, intercourse, exercise, nipple stimulation, ingestion of certain foods and drugs, and pregnancy. If a woman's prolactin level is elevated the first time it is tested, a second sample should be checked when she is fasting and non-stressed. If the prolactin level continues to be markedly elevated, it is important to look for a cause.

Ovulation and menstruation generally return within six weeks of normalizing prolactin levels. Galactorrhea takes more time and is less certain to resolve.

Hyperprolactinemia is a common problem found in up to one-third of patients with absence of menstruation and in up to 90 percent of women with galactorrhea. Observation and expectant management is appropriate for some of these women, and medical management is highly successful in others.