Evidence-Based Care Evolves: Introducing Our Progesterone Service
For years, the question of progesterone in feminising hormone therapy has been marked by a frustrating gap: trans women reporting benefits, but empirical evidence failing to materialise. That's changing. Recent research provides the first objective evidence supporting what the community has long reported, and it's prompted us to evolve our UK practice accordingly.
As the only CQC Outstanding registered provider of hormone therapy to the trans community aged 16+, we've always prioritised evidence-based care. Today, we're announcing the introduction of progesterone as part of our feminising gender-affirming hormone therapy (GAHT) pathway for UK based patients, a decision grounded in a rigorous review of emerging research and our commitment to offering safe, effective treatment options.
The Breakthrough Evidence
Dreijerink et al.'s presentation of their randomised controlled trial at EPATH 2025, represents a watershed moment. This is the first study to use objective measures - 3D breast volume measurements - in trans women, and the results are significant. Over 12 months, trans women receiving progesterone alongside estradiol showed breast volume increases of between 13 and 37 per cent compared to the estradiol-only control group, with results varying by dosage. These differences reached statistical significance (p<0.05), providing empirical validation for what has long been anecdotal.
This matters because previous research consistently returned null results. Wierckx et al. (2014) and T'Sjoen et al.’s (2019) reviews found no empirical evidence of increased breast development with progesterone, though the study methodology available at the time suffered from small sample size, brief follow up and there were difficulties with the measurement tools utilised.
The gap between lived experience and research findings left many trans women - and their healthcare providers - in uncertain territory.
Why previous findings are not applicable to this population
Much of the caution around progesterone stemmed from the 1990s Women's Health Initiative, which found increased risks of breast cancer, cardiovascular events, and stroke in postmenopausal cisgender women using combined oestrogen-progestin HRT (Rossouw et al., 2002). However, as Bahr et al. (2024) emphasises, generalising these findings to trans women may not be possible. Trans women have distinct developmental experiences of hormone production, different breast tissue development, and vastly different lifetime exposure to oestrogen and progesterone. Trans-specific evidence was needed to make a meaningful assessment - and now we have it.
Setting Realistic Expectations
Evidence-based care means being transparent about both benefits and limitations. The Dreijerink Study reported side effects including tiredness (44%), breast and nipple tenderness (27%), and mood changes (22%). Importantly, there were no treatment-related serious adverse events, and progesterone was concluded to be safe. These are manageable effects that many will find acceptable given the potential benefits, but they warrant informed discussion.
It's also important to note that progesterone is currently available to patients who have been on feminising hormone therapy for at least one year. The study also had the specific parameter that participants had undergone vaginoplasty or orchiectomy, which means we need further research to understand progesterone's role without surgical intervention. We will always assess each patient’s individual circumstances carefully before deciding whether progesterone is the right option.
Our Approach: Expertise, Rigour, and Safety
The literary review was carried out by Gender Plus' research team. We plan to monitor the progress and any side effects of progesterone at three and six month intervals. Patients will be started on a low dose which will be titrated where clinically required.
Our CQC Outstanding rating reflects our commitment to the highest standards of care, safety, and patient outcomes. Introducing progesterone represents the evolution of that commitment: we move when the evidence moves, always prioritising the wellbeing of our patients and their informed choice.
What This Means for Patients
If patients are currently receiving feminising hormone therapy with us and they are interested in exploring progesterone, we invite them to discuss this option at their next appointment. We will assess individual circumstances, discuss realistic expectations, and determine whether progesterone aligns with the patients’ goals and medical history.
This is cautiously optimistic territory. The evidence is promising, the safety profile is acceptable, and we now have objective data supporting a treatment many have long sought. But as with all aspects of gender-affirming care, individualised assessment and ongoing monitoring remain paramount.
Get in Touch
Contact us to book a consultation or to discuss the possibility of adding progesterone to your existing hormone regime. Our expert team is here to lend their support with evidence-based, outstanding care.
