Anyone can drink breast milk, it's not harmful. I think it's more a moral issue. Breast milk is for babies, not grown ups...eww.
And, yes, a woman can produce milk without being pregnant by taking the hormones that cause women to lactate. This is what "wet nurses" used to do. A wet nurse would work in the hospital nursery and nurse babies. This practice isn't done anymore in developed countries. Also, in the case of an adoptive mother who's just adopted a newborn, she can take a combination of hormones that will cause her to start lactating, so she can nurse her baby.
Hope this helps.