TL;DR
- Standard doses of feminising HRT do not reliably produce the same hormone levels in everyone — individual variability is substantial
- Real-world data show many trans women do not achieve guideline hormone targets, with subtherapeutic oestradiol more common than excessive levels
- Studies have found that oral oestradiol-based regimens fail to suppress testosterone below target in roughly 25–33% of patients despite oestradiol concentrations within commonly recommended ranges
- Possible contributors include individual absorption variability, conservative prescribing, limited specialist access, and infrequent monitoring — but these are not uniformly established
- The goal is not to maximise oestradiol levels — it is individualised adjustment based on measured hormone levels and clinical response
Standard doses of feminising HRT do not reliably produce the same hormone levels in everyone. What works well for one person may produce subtherapeutic levels in another on the same formulation and dose. This has meaningful clinical consequences — and it is one of the most underappreciated aspects of HRT management.
What real-world data shows
Multiple real-world studies suggest that many trans women do not achieve guideline hormone targets in clinical practice. A cohort study from Thailand found that among trans women using feminising HRT, the majority had hormone concentrations outside target ranges — and among those outside range, subtherapeutic oestradiol was considerably more common than excessive levels. This was a single cohort and should not be generalised across all healthcare systems, but the pattern is consistent with findings from other real-world analyses.
Separately, studies examining guideline-concordant prescribing — doses written exactly as guidelines recommend — have found these doses frequently fail to produce target hormone levels in practice. With transdermal oestradiol, standard guideline doses commonly yield subtherapeutic oestradiol concentrations. With oral oestradiol combined with antiandrogens, testosterone fails to suppress to below 50 ng/dL in roughly 25–33% of patients despite oestradiol concentrations within commonly recommended ranges.
Why standard doses don’t work equally for everyone
Individual variability in absorption and metabolism is the central issue. Oral oestradiol has highly variable bioavailability — with differences of several-fold between individuals on the same dose. First-pass hepatic metabolism, gut absorption, and differences in oestrone conversion contribute substantially to this variability; body composition and other physiological factors may also play a role. A dose that produces therapeutic levels in one person may produce substantially different levels in another.
Possible contributors to inadequate dose adjustment in clinical practice include conservative prescribing culture, limited access to specialist trans healthcare, reduced familiarity with HRT optimisation among generalist prescribers, and infrequent monitoring that fails to detect subtherapeutic levels. These are plausible explanations supported by clinical observation rather than uniformly established findings — but the pattern across studies is consistent enough to be clinically meaningful.
What adequate monitoring looks like
Endocrine Society guidelines recommend measuring oestradiol and testosterone every three months during the first year of HRT, then every six to twelve months once stable. In some settings, monitoring occurs less frequently than these recommendations suggest, or results are interpreted without reference to appropriate targets.
The goal is not to maximise oestradiol levels or chase numbers for their own sake. The goal is to achieve oestradiol and testosterone within target ranges, assess clinical response, and make individualised adjustments based on measured results. That requires measuring regularly and interpreting results against appropriate benchmarks — not assuming a standard dose is producing the intended effect.
What this means in practice
If you have been on a stable dose for months or years without recent hormone testing, you have limited objective information about whether your current regimen is achieving its intended hormonal targets. If your testosterone has only ever been reported against a male reference range, you may not know whether it is within recommended treatment targets. If your oestradiol has never been measured at a consistent, known point in your dosing cycle — trough timing matters most for injectable regimens, which fluctuate significantly between doses — you may not have a reliable picture of your baseline levels.
You have the right to ask for your numbers. You have the right to understand what they mean. You have the right to care that is individually adjusted, not just initiated.
⚠️ Clinical note: The evidence supports that standard doses produce variable outcomes and many patients do not achieve hormone targets in practice. It does not support a universal claim that most trans women are under-dosed, nor does it imply that higher levels are inherently better. Individualised adjustment based on measured levels and clinical response is the appropriate goal.
Sources
- Hiransuthikul A, Janamnuaysook R, Getwongsa P, et al. Estradiol and Testosterone Concentrations Among Thai Transgender Women in a Transgender-Led, Integrated Gender-Affirming Care and Sexual Health Clinic: A Real-World Analysis. Transgend Health. 2022;7(6):539–547.
- Carlson SM, Dominguez C, Jeevananthan A, Crowley MJ. Follow-Up Estradiol Levels Based on Regimen Formulation With Guideline-Concordant Gender-Affirming Hormone Therapy. J Endocr Soc. 2025;9(3):bvae205.
- Misakian AL, Ariel D, Sullivan EA, et al. Injectable Estradiol Monotherapy Effectively Suppresses Testosterone in Gender-Affirming Hormone Therapy. Endocr Pract. 2025;31(11):1462–1469.
- Hembree WC, Cohen-Kettenis PT, Gooren L, et al. Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2017;102(11):3869–3903.
