Research Finds Progesterone Enhances Breast Growth in Transgender Women Undergoing Hormone Therapy

Recent research conducted by Amsterdam University Medical Centers indicates that incorporating progesterone into gender-affirming hormone therapy can significantly promote breast growth in transgender women. The study involved 90 participants who were on estrogen treatment, and their breast development was meticulously measured using advanced 3D scanning techniques. The results revealed an increase in breast volume of up to 37%, with many participants reporting increased satisfaction with the size and shape of their breasts.

Traditionally, feminizing hormone therapy involves the use of estrogen, which can induce some degree of breast development, but often not enough to eliminate the need for surgical augmentation. Progesterone, a key hormone in cisgender women responsible for breast development, had not been widely used in transgender hormone protocols due to limited evidence of its safety and effectiveness.

The trial, which took place between 2021 and 2024, aimed to fill this knowledge gap. Participants who received progesterone alongside estrogen experienced notable breast growth and reported increased body satisfaction. The largest growth was observed in individuals who also increased their estradiol dosage. Some side effects such as tiredness, breast and nipple sensitivity, and mood swings were reported, but overall, progesterone was deemed safe for use within a controlled trial setting.

Leading researcher Koen Dreijerink emphasized that these findings support the safety and efficacy of progesterone for transgender hormone therapy. He stated, "Our results show that progesterone is safe and effective for transgender people, and we are now able to prescribe it in a clinical setting for those who have been on estradiol for at least a year. We hope this contributes to improved hormone treatments for transgender individuals."

The study also highlighted that progesterone might enhance the hormonal treatment experience, allowing some individuals to achieve desired breast development without surgical intervention. However, long-term effects and side effects are still being studied, with researchers advising participants to take progesterone at night due to its sedative effects. Moving forward, ongoing research aims to better understand the long-term safety and benefits of including progesterone in gender-affirming therapy.