When a transgender woman told doctors at a hospital in New York that she wanted to breastfeed her pregnant partner’s baby, they put her on a regimen of drugs that included an anti-nausea medication licensed in Britain and Canada but banned in the United States.

Within a month, according to the journal Transgender Health, the woman, 30, was producing droplets of milk. Within three months — two weeks before the baby’s due date — she had increased her production to eight ounces of milk a day.

In the end, the study showed, “she was able to achieve sufficient breast milk volume to be the sole source of nourishment for her child for six weeks,” according to the journal.

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Dr. Tamar Reisman and Zil Goldstein, a nurse practitioner, of the Mount Sinai Center for Transgender Medicine and Surgery in New York, say the case illustrates that, in some circumstances, modest but functional lactation can be induced in transgender women who did not give birth or undergo surgery.

“We believe that this is the first formal report in the medical literature of induced lactation in a transgender woman,” said the study’s authors, Reisman and Goldstein, a transgender activist and program director at the centre. They were not immediately available for comment Thursday.

Some hailed the case study, published in January, as a “breakthrough” for transgender families; others called it “dangerous” and “disturbing.” But if confirmed in wider studies, the regimen could represent a next major stage in transgender parenthood. Transgender men like Thomas Beatie, Trystan Reese and Kaci Sullivan have made headlines by giving birth. But breastfeeding for transgender women had not been officially documented.

Breast milk is considered the best form of nutrition for infants. Breastfed babies have healthier immune systems, score higher on IQ tests and may be less prone to obesity than other babies. Advocacy campaigns have noted that the practice facilitates mother-child bonding, and saves families from spending money on infant formula. The World Health Organization, in setting new international benchmarks for children’s growth, has said that breastfeeding is the biological norm.

But in the case published in Transgender Health, it is not known whether breast milk from this kind of induced lactation is equivalent to milk produced after giving birth by women who are not transgender.

Dr. Joshua D. Safer, medical director of transgender medicine and surgery at Boston Medical Center, called the study “a very big deal” and said he expected it to become very popular among transgender women.

“It’s out there on internet forums, but there’s a lot on the internet that’s true or untrue to varying degrees,” he said in an interview with the weekly magazine New Scientist. “It’s a very big deal to have this recorded in a reliable document.”

Others were skeptical about the study and what it could mean for transgender women.

“We all want to have the same experiences as women,” Maria Clifford, 38, a British transgender mother who has been using a surrogate to breastfeed her child, said Thursday. “We need further testing and evidence to show that these drugs aren’t going to cause harm to the baby.”

“Breast milk is the most important product for the development of a child,” Clifford added. “We need to make sure it’s pure and hormone free.”

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The transgender woman in the experiment — neither she, her partner nor their hometowns were identified — approached the doctors for hormonal medications in 2011 as part of transgender treatment. She had been receiving it for several years before she began breastfeeding, according to the study. She had not had gender-reassignment surgery nor breast augmentation.

She took on the responsibility of breastfeeding because her partner, who was five months pregnant when they approached the doctors, did not want to.

As part of the lactation treatment, the woman stimulated her chest using a breast pump while she took female hormones including progesterone and estradiol, as well as an anti-nausea drug called domperidone, known to increase breast milk production.

The woman obtained domperidone from Canada. Though used in many countries, including in Britain, it has been banned in the United States because of Food and Drug Administration concerns about its associations with cardiac arrest and sudden death.

Previous studies with transgender women have reported only the basic framework for what is known as nonpuerperal induced lactation, the process by which women are stimulated to lactate.

“There have been self-reported cases online of transgender women trying to DIY regiments to induce breastfeeding, but this is the first case of induced functional lactation in academic literature,” Reisman was quoted in the journal as saying.

The study’s authors said the woman was able to exclusively breastfeed the infant for six weeks. During that time, a pediatrician reported that the child’s growth, feeding and bowel habits were developing normally.

At six weeks, the woman began to supplement breastfeeding with a formula because of concerns about insufficient milk volume.

The woman’s hormone regimen was generally considered safe and similar to ones used on mothers who are unable to produce their own milk. But she continued to take the drug spironolactone, which blocks testosterone and “is excreted in human milk,” the study said.

The baby is now 6 months old, the study’s authors said. They wrote that it was unclear which parts of the regimen were most beneficial to producing milk.

Future areas of study include “the optimal dosing of estradiol, progesterone and galactogogues in inducing lactation, as well as the optimal frequency and duration of pump use,” they said.