I know, I am semi-retarded if I couldn't find this out through research. But can women only give milk if they are pregnant/recently given birth? It's coming into play in a story I'm working on...
Actually, while it is easiest to produce milk after giving birth, anyone can produce milk if there is enough nipple stimulation.
One option when adopting a baby is to have the baby "nurse" while drinking milk from a tube. Eventually, the adoptive mom's milk will come in and the mom and child will have full bonding through nursing. Some adoptive mom's get pro-lactin from their doctors to help the process along, but it isn't absolutely necessary.
My husband reported that for almost a year after I weaned my last child he would "get a little something" when sucking on my breasts... In some ways, I wish he hadn't told me....
I think I saw a thread on this not long ago on the How To board, with some links to other sources of info on the topic. Try running a search here on the word 'lactate' or 'lactating.'
I think the correct term for it is relactating, because the attempt is usually much more likely to succeed if the woman has had a baby before, even if it was ten years ago.
This is a bit of reality you may choose to ignore in your story writing: The hormone prolactin is helpful when trying to relactate, but it has a supressing effect on the woman's sex drive. Chances are, any woman taking prolactin wouldn't be very interested in sex. But 99% of readers out there won't know or care about that.
You may want to do a search on "Wet-Nurse". There are medical anomolies that happen, some women that have had their ovaries removed can still actively produce milk. There are also "herbal stimulants" that will help with milk production.
If you can be bothered to suck for long enough (no jokes please), even men can lactate. Everyone's got a little something in them, it's just a question of sucking long enough to get it out.
Yes I am well aware of how many double-entendres could be made there. Please don't for everyone's sanity.
My ex-wife never really quit lactating after the birth of our twin boys. For years she continued to produce milk...mainly cause I never really left her alone. (grinning).