Progesterone can boost breast growth in transgender women, study finds

Adding the hormone progesterone to hormone therapy leads to breast growth in transgender women, according to a study conducted by Amsterdam UMC. Participants took progesterone for one year.

To evaluate the effects of progesterone, Koen Dreijerink, endocrinologist at Amsterdam UMC, and his team studied 90 participants using 3D scanning to measure breast volume. “We observed up to a 30 percent increase in breast volume,” said Raya Geels, a PhD candidate at Amsterdam UMC and the study’s first author.

“Participants using progesterone were more satisfied with the size, shape, and growth of their breasts than those not using it,” Geels said. The greatest increase occurred in participants who also increased their estradiol dose.

“Our results show that progesterone works and has limited side effects for transgender individuals,” said Dreijerink. “We can now prescribe it in a research setting to people who have been using estradiol for at least a year. We hope these findings lead to improved hormone treatments for transgender individuals.”

Progesterone, alongside estradiol, is one of the two main female sex hormones and is known to promote breast growth in cisgender women. Until now, it had not been prescribed to transgender women due to limited evidence of its effectiveness and safety. Common side effects included fatigue, breast and nipple tenderness, and mood swings.