What is prolactin?

Marvin Bergsneider, MD
Prolactin is a hormone that stimulates the breasts to make milk. At the end of pregnancy, when estrogen levels are high, and you have prolactin, a mother's breast glands start getting ready for childbirth. After childbirth, this allows her to feed her child. One of the main functions of prolactin is breast milk production. But nature also doesn't want a new mother to get pregnant again, so while a mother is breastfeeding her child, typically a mother doesn't have menstrual periods. That's because prolactin decreases the amount of sex hormones that are released by the pituitary gland and stops menstrual periods during breastfeeding.

The release of prolactin is regulated by a chemical released by the brain called dopamine. As dopamine is released by the brain, it actually shuts down the release of prolactin. So when your body needs more prolactin, less dopamine is released. If a woman has an excess of prolactin production, essentially the female body thinks it just had a baby. The woman is not going to have menstrual periods and sometimes she may even have breast milk production.

Since men don't have menstrual periods, only the second effect -- the decrease of sex hormones -- occurs, and a man can have low testosterone. Unfortunately, that isn't clinically evident, or men don't see their doctors about it. Even if they do and a low testosterone is found, a prolactin level isn't drawn. It's important if you're a male with low testosterone to ask your doctor to get your prolactin levels drawn, because in some cases they're going to find a pituitary tumor. That's something that can be fixed if it's discovered early on.

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