With considerable dedication and preparation
The Mayo Clinic answers this question:
I’m adopting a newborn, and I’d like to breastfeed the baby when I bring him home. Can I produce breast milk if I haven’t been pregnant?
Neither the question nor the answer mentions “woman” but perhaps we can assume it’s assumed.
With considerable dedication and preparation, breastfeeding without pregnancy (induced lactation) might be possible.
Normally, the natural production of breast milk (lactation) is triggered by a complex interaction between three hormones — estrogen, progesterone and human placental lactogen — during the final months of pregnancy. At delivery, levels of estrogen and progesterone fall, allowing the hormone prolactin to increase and initiate milk production.
Induced lactation depends on the successful replication of this process. If you have months to prepare, your health care provider might prescribe hormone therapy — such as supplemental estrogen or progesterone — to mimic the effects of pregnancy. Hormone therapy may last for months.
About two months before you expect to start breastfeeding, you’ll likely stop hormone therapy and begin pumping your breasts with a hospital-grade electric breast pump. This encourages the production and release of prolactin. At first, pump for five minutes three times a day. Work up to pumping for 10 minutes every four hours, including at least once during the night. Then increase pumping time to 15 to 20 minutes every 2 to 3 hours. Continue the routine until the baby arrives.
In the absence of pregnancy it’s iffy, and a lot of trouble. I think it’s safe to conclude that in the absence of female breasts it’s a lot more iffy. A lot more.
We await the results of controlled experiments to study the psychological effects on babies who have been suckled at the nipples of male parents; maybe two of them taking turns on that particular job. Maybe more than two. (Think of a number and double it.)
Unfortunately it looks like most research articles related to induced lactation are behind paywalls, but yeah even some otherwise normal (in the statistical sense) women can’t produce enough milk to adequately nourish an infant without supplementation. I could try hunting further, but after a quick search I can’t seem to find much in the way of articles investigating the exact nature of the hormones used (lactation induction in women doesn’t actually always involve adding hormones, so relatively small sample size to start with) or the effects of supplemental hormones on the milk quality or the infants.
But hey, let’s look on the bright side: the scarcity of research into the effects of induced lactation on mother and infant may be righted now that males are going to be impacted rather than just those mysterious, unknowable women. Sigh.
We became parents through adoption and my wife really wanted to try to breastfeed, having been told that some women were able to do it. The protocol involved preparation a couple months in advance & required significant dedication to pumping as noted above; it’s not for everyone. She was ultimately successful, though she also required supplementation with formula throughout the process. As far as I recall, she wasn’t getting added hormones – maybe briefly at the beginning? Of course, she had the luxury of not having to work for an extended period of time, and if the protocol hadn’t worked for whatever reason, we would have moved on. Breastfeeding was important to her, but it’s not like she lost sight of the fact that the primary focus was on what was best for the baby. We knew from the outset that it might not work, just as it doesn’t always work for women who’ve given birth; it wasn’t about any kind of self-validation.
Putting the baby first – what a concept!
I’m glad she was successful.