Prolactin is a pea-sized hormone secreted from the anterior lobe of the pituitary gland in the brain. It is commonly known as the 'milk hormone.' This hormone is primarily responsible for breast milk production, the breastfeeding process, and the development of breast tissue, especially in women. In addition to milk production and secretion, prolactin also has significant effects on the menstrual cycle and general reproductive functions. It also plays a role in regulating sexual desire and libido, making it an important part of reproductive health. Prolactin levels in the bloodstream can be measured with a blood test.