Breastmilk

Men can actually begin lactating relatively easily even without the need for medication. One method involves stimulating the nipples with sucking for an extended period of time. Eventually they'll just start lactating.

Another method is by using starvation combined with a nutritional comeback. Survivors of certain prisoner of war "camps" were thus able to experience this "miracle." This is due to how hormone-producing glands are able to recover faster than the (hormone-absorbing) liver from starvation resulting in soaring hormone levels.