Prolactin

Prolactin is a hormone produced by a small gland at the base of the brain called the pituitary gland. Its most recognized function is stimulating the breasts to produce milk during and after pregnancy — prolactin levels rise dramatically during the third trimester and remain elevated while a person is breastfeeding, which also tends to suppress ovulation and delay the return of menstrual periods.

Outside of pregnancy and breastfeeding, prolactin levels are normally low. But the pituitary gland can sometimes produce excess prolactin even when a person isn't pregnant — a condition called hyperprolactinemia. When prolactin is too high, it can interfere with the hormonal signals needed for regular ovulation, leading to irregular periods, infertility, or in some cases the complete absence of menstruation. It can also cause nipple discharge in people who are not breastfeeding, which is one of the reasons prolactin levels are tested when nipple discharge appears unexpectedly.

Elevated prolactin is often caused by a small, benign tumor on the pituitary gland called a prolactinoma. While that sounds alarming, prolactinomas are very common and almost always non-cancerous, and they typically respond well to medication that brings prolactin levels back to normal without the need for surgery.

Prolactin is worth knowing about because abnormal levels can explain symptoms that are sometimes difficult to connect to a cause — irregular periods, unexplained nipple discharge, or difficulty conceiving. A simple blood test can measure prolactin, and if levels are elevated, further evaluation can identify the cause and guide appropriate treatment.

For breastfeeding women, prolactin is essential, and understanding its role helps explain why nursing tends to delay the return of fertility. For women who are trying to conceive and experiencing hormonal disruption, prolactin testing is often part of the standard workup — and if hyperprolactinemia is the culprit, effective treatment is available.