Prolactin, also known as the milk hormone, is a pea-sized hormone secreted by the anterior pituitary gland in the brain. It is responsible for milk production in women, as well as breastfeeding and breast tissue development.

In addition to milk production and secretion, prolactin, also known as the "milk hormone" in society, plays a role in the menstrual cycle and reproductive functions. Supporting sexual desire and libido, prolactin is important for reproductive health. A blood test is used to measure the amount of prolactin in the blood.