Most people believe that a woman cannot give milk until she has had a child, much like cows. This is, in most cases, untrue. Almost any woman can give milk, if she has gone through puberty, and even if a woman has had a child and have stopped producing milk, she can give milk again without having another child. All it takes is someone else to suck on the nipple on a regular basis. This signals the breast to start milk production, and the breast will give milk within a few days, if sucking continues.

If you are going to try this, you should know the following:

1) The sucking needs to be firm, not rough, and it may hurt a little.
2) The breast being sucked on will grow larger than the other, so make sure both breasts are given equal attention, or you may end up lop-sided.
3) The breasts giving the milk will hurt or ache during the day as milk is produced.
4) The breasts may grow heavier and become firmer.
5) The amount of milk may not be much at first, but will increase for as long as sucking continues.
6) Larger breasts work better for this than smaller breasts.
7) The milk is odorless and almost tasteless, and comes out as a slightly watery white, looking, for a while, like semen.
8) The while the partner sucks, he/she needs to know when the point comes that the breast hurts too much or is too sore to continue. The pain and soreness lasts for a while, and is not a very fun thing to have to endure.

If, after a few days, nothing happens but soreness, stop and try again in a few days. If nothing happens, then the breasts are incapable of giving milk yet. The woman may not have enough hormones in her system to induce milk production. Wait until she gets pregnant, and then try again. Partners: Please do not try this without the woman's permission. Some women may be self-conscious about doing this, so make sure she's comfortable with the act before continuing.

It is possible to breastfeed an adopted baby. Lactation is controlled by prolactin (which makes the milk) and oxytocin (which releases it), which are pituitary and not ovarian hormones: even a woman who has had a hysterectomy may lactate, though the form of estrogen typically given after such a procedure - the same form found in birth control pills - is a lactation suppressant.

MizerieRose's sucking method works because prolactin and oxytocin are produced in response to nipple stimulation; a baby or a breast pump will work equally well in this. It will typically take one to four weeks for human or mechanical stimulation to induce lactation.

Hormonal therapy can also be used, including estrogen administered in a way to trick the body into thinking it is pregnant. Estrogen is then withdrawn, mimicking the rapid hormonal changes following delivery. A drug such as metaclopromide is then given to enhance prolactin production, and sucking stimulation is also used at this point. This method usually begins to produce milk after five to thirteen days.

There are also natural methods that can be used to help induce lactation. Fenugreek and blessed thistle can sometimes be found in health food stores or other locations with a good selection of herbal supplements. Domperidone, a drug given for gastric problems, has a side effect of increasing lactation.

Sources:
http://www.surrogacy.com/medres/article/lac.html
http://www.submission.net/lactation.html
http://www.adoptivebreastfeeding.com/