Men have mammary glands, and they can produce milk—but not enough to feed a baby. In fact,
male lactation is usually caused by an interference with prolactin, the hormone necessary to produce milk. The most common trigger is a tumor in the pituitary gland, but it can also be spurred by heart medication (digoxin), opiods or hormone treatments for prostate cancer, write Goldberg and Leyner in
Why Do Men Have Nipples?. In rare cases, extreme starvation can throw off hormone levels and also cause male breasts to produce a small amount of milk.
