Human male breastfeeding is possible, but production of the hormone prolactin is necessary to induce lactation, so male lactation does not occur under normal conditions.
Domperidone is a drug that can be used to increase lactation.
Male lactation has also been seen during recovery from starvation. This may be because glands that produce hormones recover faster than the liver, which absorbs hormones, leading to high hormone levels.
Spontaneous production of milk not associated with childbirth, known as galactorrhea, can occur in males and females.