Unusually copious secretion of breast milk when a mother is feeding her baby or continuing secretion of milk after breast feeding ceases. The condition is occasionally seen in women without babies and in men. In the women it may not be due to disease, but in many of them, and in all of the men, the cause is a disorder of the thyroid or pituitary glands, kidney or liver failure or certain rare tumours secreting PROLACTIN. It can also be a rare side-effect of certain drugs.