Male lactation refers to the phenomenon of milk production in men; the volume of milk, however, is considerably low compared to that of a lactating female. It is commonly caused by hormonal treatments — usually estrogen — given to prostate cancer patients, and in some cases, it can be a side effect of several atypical antipsychotic medications. Several lifestyle factors have also been attributed to male lactation, particularly in stress levels and diet. In most cases, this condition, which was first reported in the mid 1800s, is considered to pose no risks to an individual's health.

Side effects of atypical antipsychotic medications may include male lactation.

Males who have gone through a sex reassignment surgery (SRS) might lactate as a side effect of the hormones they take as part of the procedure. Male lactation can also be caused by extreme stress due to demanding physical activities and severe starvation. At the end of World War II, male survivors of the liberated Nazi concentration camps were known to produce milk. Some prisoners of war returning from the Vietnam and Korean wars also experienced male lactation. According to recent studies, it is possible to induce lactation in males through constant stimulation of the nipples over a certain period of time.

Male lactation may be caused by hormonal treatments that are given to prostate cancer patients.

Some experts believe that male lactation can be triggered by adequate consumption of galactogogues or lactogogues, agents that promote lactation usually found in products that boost milk production in nursing mothers. These substances can be synthetic, endogenous, or plant-derived. The most commonly-cited sources are herbal, although pharmaceutical medications are considered more effective and are usually available by prescription.

Some prisoners of war have experienced male lactation upon their return home.

Several medical conditions can produce symptoms similar to male lactation, although their processes are unrelated to normal milk production. Galactorrhea, a milky form of nipple discharge, is often caused by excess levels of prolactin, a hormone secreted by the pituitary gland. In men, it is associated with hypogonadism, or testosterone deficiency, and occurs with gynecomastia, an enlargement of the breasts in males. A lesion in the pituitary gland might also be the cause of male lactation.

Male lactation may occur with gynecomastia, or enlargement of the breast tissue.

Treatment methods for galactorrhea vary, depending on the cause. If the condition is due to an underactive thyroid gland, levothyroxine can be taken to counter insufficient hormone production. A tumor in the pituitary gland can either be shrunk or excised through surgery.

Male lactation can be caused by extreme stress and demanding physical activities.