Which hormone promotes breast development and milk production?

Prolactin is the hormone responsible for promoting breast development and stimulating milk production in mammals. It is secreted by the anterior pituitary gland and plays a crucial role during and after pregnancy. Prolactin levels increase significantly during pregnancy, preparing the mammary glands for milk production. After childbirth, it stimulates the production of milk in response to the sucking of an infant, facilitating breastfeeding.

This specific function distinguishes prolactin from the other hormones listed. Growth hormone primarily influences growth and metabolism, while thyrotropin (also known as thyroid-stimulating hormone or TSH) regulates the thyroid gland's function. Luteinizing hormone plays a significant role in regulating the menstrual cycle and ovulation, rather than directly affecting breast development and milk production. Thus, prolactin is uniquely suited for the specific functions related to lactation.