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The pituitary gland is responsible for producing the hormone prolactin, which regulates milk production in breast-feeding women. A hormone-producing tumor called a prolactinoma increases prolactin levels and can cause unexpected lactation and other symptoms.

A prolactinoma, a hormone-producing tumor that generates excess levels of the hormone prolactin, is the most common type of pituitary tumor. Prolactinomas are, the majority of times, benign (non-cancerous) tumors, but they do require treatment to alleviate symptoms.

Prolactin is a hormone produced by the pituitary gland, and like most hormones its role in the body is complex. Its most familiar job, however, is to stimulate lactation in breast-feeding women. (Both men and women produce prolactin, although its role in men’s health is not completely understood.) Prolactin levels rise during pregnancy to prepare for breast-feeding. In new mothers, prolactin levels rise when the baby nurses, and the elevated hormone level causes increased milk production. When a new mother does not breast-feed, her prolactin levels fall back to normal, pre-pregnancy levels.

High levels of prolactin in individuals who are neither pregnant nor breast-feeding, however, can lead to unexpected milk production, irregular periods, sexual dysfunction, and infertility. Many things may cause an increase in prolactin production, with the most common cause being a prolactinoma. Prolactinoma is diagnosed most often in women, although it can occur in men as well. (See Diagnosing and Treating Prolactinoma.)

What Causes Prolactinoma?
The majority of prolactinomas do not appear to have a genetic connection, and it is unknown what causes them.

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Reviewed by: Georgiana Dobri, M.D.
Last reviewed/last updated: December 2020
Illustration by Thom Graves, CMI