Study analysis · Cureus · 2025
About 1 in 4 transgender women on standard hormone therapy still exceeded common sports testosterone thresholds after 1–2 years (absolute: 19.5–25.0%).
In a retrospective study, many transgender women taking estrogen and spironolactone got very low testosterone, but about one quarter still had levels above the limits used for women's sports after 1–2 years.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study is like a diary of testosterone levels in a group of transgender women over time. It can tell us what happened to them, but because there was no comparison group and no randomization, it can't prove what caused the changes or whether it would work the same for everyone.
What’s the bottom line?
Doctors checked testosterone levels in transgender women taking standard hormone therapy (estrogen plus spironolactone). They wanted to see how many get their testosterone low enough for women's sports rules.
How strong is this study?
The study has a good number of people at first, but many dropped out by two years, and it's from one clinic. Also, they didn't check if people actually took their medications. So we should be careful about trusting the exact numbers for everyone.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
31 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=261)+14.6/20
- Follow-up+10/10
100 / 100
23 / 100
- P-valuesno p-values reported
- Effect sizeno effect size reported
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 545 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. This is a retrospective single-arm observational study with no control group or randomization. It can only describe changes in testosterone levels over time within the same individuals, but cannot establish that GAHT causes the observed testosterone suppression, nor can it rule out confounding by adherence, other treatments, or natural variation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding sources were declared; no industry ties identified in the provided text.
The manuscript does not include a conflict of interest or funding section, nor author affiliations or names. While no conflicts are apparent from the text, the absence of disclosure prevents a full assessment.
Key takeaways
- 01
After 1 year, the typical (median) testosterone was 0.52 nmol/L, but the average (mean) was 3.39 nmol/L.
- 02
About 19.5% (absolute) had testosterone above 5 nmol/L and 23.8% (absolute) above 2.5 nmol/L.
- 03
After 2 years, median was 0.43 nmol/L and mean 3.90 nmol/L; 22.3% (absolute) above 5 nmol/L and 25.0% (absolute) above 2.5 nmol/L.
- 04
This means that while many transgender women on standard hormone therapy reach low testosterone levels, about 1 in 4 (absolute) do not get below common sports thresholds of 2.5 or 5 nmol/L after 1-2 years.
- 05
The study did not include athletes specifically, so it cannot prove how this affects fair competition.
Surprising findings
- Median testosterone was very low (0.52 nmol/L at 12 months) but mean was over six times higher (3.39 nmol/L).Most people assume mean and median are close; this huge gap means a small subset has very high testosterone, skewing the average.
- Almost one quarter did not achieve suppression below 2.5 or 5 nmol/L after 1–2 years.Sports guidelines often treat 12–24 months of testosterone suppression as sufficient, but this study shows a substantial minority remain above common thresholds.
- The proportion above 5 nmol/L was slightly higher at 24 months (22.3%) than at 12 months (19.5%).Longer treatment is generally expected to lower testosterone further, but this study saw no clear improvement—and the mean actually rose.
- The study discussion cites recent publications suggesting testosterone suppression post-puberty does not negate male performance advantage.This goes beyond the study's own data and implies that even successful testosterone suppression may not resolve fairness debates.
- Mean testosterone in trans women on GAHT (3.39–3.90 nmol/L) was higher than a typical cisgender female range (0–1.7 nmol/L).Standard GAHT aims to suppress testosterone, but the average in this cohort remained above typical cis female levels.
Practical takeaways
For transgender women on GAHT, monitor testosterone at 12 and 24 months as part of routine care; if levels remain above target, discuss adherence, dosing, or alternative regimens with a clinician.
This was a retrospective single-center study with no sport participation data; it does not prove that changing regimen will lower levels or improve fairness.
medium confidenceFor sports policymakers, do not assume all transgender women on standard GAHT will meet common testosterone thresholds after 12–24 months—about 1 in 4 may not.
The study did not measure athletic performance or competitive advantage, and loss to follow-up was high at 24 months (112 of 261).
low confidenceFor athletes and coaches navigating eligibility, eligibility often requires documented testosterone levels; individual variation means some may need longer or different treatment to meet a given threshold.
The study is not athlete-specific and cannot predict any individual's response or eligibility outcome.
low confidenceFor content creators, use this study to discuss variability and limitations, not to claim it proves fairness or unfairness in sports.
The study is observational and the authors explicitly state it cannot assess competitive advantage.
high confidenceWhy this study matters
Median vs. mean: two very different stories
At 12 months, median testosterone was 0.52 nmol/L (95% CI 0.47–0.73) but mean was 3.39 nmol/L (95% CI 2.63–4.15). At 24 months, median was 0.43 nmol/L (95% CI 0.35–0.66) and mean was 3.90 nmol/L (95% CI 2.51–5.29). This positive skew means most patients suppressed well, but a subset had much higher levels.
It shows why averages can mislead: the 'typical' patient is very low, but the average is pulled up by a minority.
About one quarter missed common sports thresholds
At 12 months, 19.5% (95% CI 15.2–24.8) had testosterone above 5 nmol/L and 23.8% (95% CI 19.0–29.3) above 2.5 nmol/L—absolute percentages. At 24 months, 22.3% (95% CI 15.6–30.9) were above 5 nmol/L and 25.0% (95% CI 17.9–33.8) above 2.5 nmol/L.
Many sports policies assume a year or two of hormone therapy reliably brings testosterone below eligibility limits. This study suggests that's not true for everyone.
Longer treatment didn't clearly improve threshold attainment
The proportion above 5 nmol/L was 19.5% at 12 months and 22.3% at 24 months; above 2.5 nmol/L it was 23.8% and 25.0%. The confidence intervals overlap, so no clear improvement. Median dropped slightly (0.52 to 0.43 nmol/L) but mean rose (3.39 to 3.90 nmol/L).
Guidelines often require 12–24 months of suppression, but more time may not guarantee lower testosterone for all.
Mean testosterone remained above typical cisgender female range
The study notes mean testosterone of 3.39–3.90 nmol/L, compared with a typical cisgender female range of 0–1.7 nmol/L from a meta-analysis. The median was much lower, near 0.5 nmol/L.
It raises questions about whether standard GAHT fully normalizes testosterone levels to typical cisgender female ranges in all patients.
This study cannot answer fairness or competitive advantage
The authors explicitly state participation in sport was not an inclusion criterion and no sport participation data were available. There was no control group, it was retrospective, single-center, and only 112 of 261 patients remained at 24 months. The study measured testosterone levels, not athletic performance.
Headlines often leap from hormone levels to fairness in sports, but this study cannot prove or disprove competitive advantage.
Real-world 'typical use' may explain high levels
The authors note the retrospective data likely reflect typical use rather than perfect use, and nonadherence to estradiol or spironolactone could affect testosterone values. They did not exclude prior gender-affirming surgeries.
It highlights the gap between clinical trial conditions and real-world medication adherence.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Doctors checked testosterone levels in transgender women taking standard hormone therapy (estrogen plus spironolactone). They wanted to see how many get their testosterone low enough for women's sports rules.
Research results
After 1 year, the typical (median) testosterone was 0.52 nmol/L, but the average (mean) was 3.39 nmol/L. About 19.5% (absolute) had testosterone above 5 nmol/L and 23.8% (absolute) above 2.5 nmol/L. After 2 years, median was 0.43 nmol/L and mean 3.90 nmol/L; 22.3% (absolute) above 5 nmol/L and 25.0% (absolute) above 2.5 nmol/L.
What this means - more context
This means that while many transgender women on standard hormone therapy reach low testosterone levels, about 1 in 4 (absolute) do not get below common sports thresholds of 2.5 or 5 nmol/L after 1-2 years. The study did not include athletes specifically, so it cannot prove how this affects fair competition.
Examined testosterone trends in transgender women on standard gender-affirming hormone therapy (GAHT) and compared levels to women's sports eligibility thresholds.
Retrospective cohort of transgender women at one academic system (2013-2023) on estradiol and spironolactone. At 12 months (N=261), median testosterone was 0.52 nmol/L and mean 3.39 nmol/L; 19.5% had levels above 5 nmol/L and 23.8% above 2.5 nmol/L (absolute percentages). At 24 months (N=112), median was 0.43 nmol/L and mean 3.90 nmol/L; 22.3% above 5 nmol/L and 25.0% above 2.5 nmol/L (absolute percentages). About one quarter did not achieve common sport thresholds.
Methods Used
Retrospective cohort using electronic health records from one academic medical system (University of Utah), 2013-2023. Included transgender women age 18+ with gender dysphoria/transgender ICD codes and prescriptions for estradiol and spironolactone. Testosterone values drawn during routine monitoring at 12 and 24 months after first GAHT prescription. No sport participation data.
Main Finding
After 12 months on GAHT, median testosterone was 0.52 nmol/L (95% CI 0.47-0.73) and mean 3.39 nmol/L (95% CI 2.63-4.15). At 24 months, median 0.43 nmol/L (95% CI 0.35-0.66) and mean 3.90 nmol/L (95% CI 2.51-5.29). Absolute proportions above thresholds: 19.5% (95% CI 15.2-24.8) above 5 nmol/L and 23.8% (95% CI 19.0-29.3) above 2.5 nmol/L at 12 months; 22.3% (95% CI 15.6-30.9) and 25.0% (95% CI 17.9-33.8) at 24 months. About one quarter did not achieve suppression below 2.5 or 5 nmol/L.
Confidence Level
Moderate/low: retrospective single-center design, no control group, no sport participation data, high loss to follow-up at 24 months (112 of 261), possible nonadherence, no p-values or effect sizes beyond descriptive statistics. The study does not assess competitive advantage.
Study Flags
Red Flags
- •Retrospective single-center design, no control group, and no sport participation data
- •High loss to follow-up at 24 months (112 of 261), limiting long-term estimates
- •Possible nonadherence to medications and no p-values/effect sizes beyond descriptive statistics
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Median testosterone was very low (0.52 nmol/L at 12 months) but mean was over six times higher (3.39 nmol/L).
Most people assume mean and median are close; this huge gap means a small subset has very high testosterone, skewing the average.
Practical Takeaways
For transgender women on GAHT, monitor testosterone at 12 and 24 months as part of routine care; if levels remain above target, discuss adherence, dosing, or alternative regimens with a clinician.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 545 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study is like a diary of testosterone levels in a group of transgender women over time. It can tell us what happened to them, but because there was no comparison group and no randomization, it can't prove what caused the changes or whether it would work the same for everyone.
The study has a COI section but no disclosure was found. A small penalty has been applied.
Strengths
- Longitudinal data over 12 and 24 months
- Relatively large sample size at 12 months (N=261)
- Uses real-world clinical data reflecting typical use
Weaknesses
- Retrospective design
- No control group
- High attrition at 24 months (N=112)
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Doctors checked testosterone levels in transgender women taking standard hormone therapy (estrogen plus spironolactone). They wanted to see how many get their testosterone low enough for women's sports rules.
Research results
After 1 year, the typical (median) testosterone was 0.52 nmol/L, but the average (mean) was 3.39 nmol/L. About 19.5% (absolute) had testosterone above 5 nmol/L and 23.8% (absolute) above 2.5 nmol/L. After 2 years, median was 0.43 nmol/L and mean 3.90 nmol/L; 22.3% (absolute) above 5 nmol/L and 25.0% (absolute) above 2.5 nmol/L.
What this means - more context
This means that while many transgender women on standard hormone therapy reach low testosterone levels, about 1 in 4 (absolute) do not get below common sports thresholds of 2.5 or 5 nmol/L after 1-2 years. The study did not include athletes specifically, so it cannot prove how this affects fair competition.
Examined testosterone trends in transgender women on standard gender-affirming hormone therapy (GAHT) and compared levels to women's sports eligibility thresholds.
Retrospective cohort of transgender women at one academic system (2013-2023) on estradiol and spironolactone. At 12 months (N=261), median testosterone was 0.52 nmol/L and mean 3.39 nmol/L; 19.5% had levels above 5 nmol/L and 23.8% above 2.5 nmol/L (absolute percentages). At 24 months (N=112), median was 0.43 nmol/L and mean 3.90 nmol/L; 22.3% above 5 nmol/L and 25.0% above 2.5 nmol/L (absolute percentages). About one quarter did not achieve common sport thresholds.
Methods Used
Retrospective cohort using electronic health records from one academic medical system (University of Utah), 2013-2023. Included transgender women age 18+ with gender dysphoria/transgender ICD codes and prescriptions for estradiol and spironolactone. Testosterone values drawn during routine monitoring at 12 and 24 months after first GAHT prescription. No sport participation data.
Main Finding
After 12 months on GAHT, median testosterone was 0.52 nmol/L (95% CI 0.47-0.73) and mean 3.39 nmol/L (95% CI 2.63-4.15). At 24 months, median 0.43 nmol/L (95% CI 0.35-0.66) and mean 3.90 nmol/L (95% CI 2.51-5.29). Absolute proportions above thresholds: 19.5% (95% CI 15.2-24.8) above 5 nmol/L and 23.8% (95% CI 19.0-29.3) above 2.5 nmol/L at 12 months; 22.3% (95% CI 15.6-30.9) and 25.0% (95% CI 17.9-33.8) at 24 months. About one quarter did not achieve suppression below 2.5 or 5 nmol/L.
Confidence Level
Moderate/low: retrospective single-center design, no control group, no sport participation data, high loss to follow-up at 24 months (112 of 261), possible nonadherence, no p-values or effect sizes beyond descriptive statistics. The study does not assess competitive advantage.
Study Flags
Red Flags
- •Retrospective single-center design, no control group, and no sport participation data
- •High loss to follow-up at 24 months (112 of 261), limiting long-term estimates
- •Possible nonadherence to medications and no p-values/effect sizes beyond descriptive statistics
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Median testosterone was very low (0.52 nmol/L at 12 months) but mean was over six times higher (3.39 nmol/L).
Most people assume mean and median are close; this huge gap means a small subset has very high testosterone, skewing the average.
Practical Takeaways
For transgender women on GAHT, monitor testosterone at 12 and 24 months as part of routine care; if levels remain above target, discuss adherence, dosing, or alternative regimens with a clinician.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 545 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study is like a diary of testosterone levels in a group of transgender women over time. It can tell us what happened to them, but because there was no comparison group and no randomization, it can't prove what caused the changes or whether it would work the same for everyone.
The study has a COI section but no disclosure was found. A small penalty has been applied.
Strengths
- Longitudinal data over 12 and 24 months
- Relatively large sample size at 12 months (N=261)
- Uses real-world clinical data reflecting typical use
Weaknesses
- Retrospective design
- No control group
- High attrition at 24 months (N=112)
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study has a good number of people at first, but many dropped out by two years, and it's from one clinic. Also, they didn't check if people actually took their medications. So we should be careful about trusting the exact numbers for everyone.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
31 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=261)+14.6/20
- Follow-up+10/10
100 / 100
23 / 100
- P-valuesno p-values reported
- Effect sizeno effect size reported
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 545 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. This is a retrospective single-arm observational study with no control group or randomization. It can only describe changes in testosterone levels over time within the same individuals, but cannot establish that GAHT causes the observed testosterone suppression, nor can it rule out confounding by adherence, other treatments, or natural variation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding sources were declared; no industry ties identified in the provided text.
The manuscript does not include a conflict of interest or funding section, nor author affiliations or names. While no conflicts are apparent from the text, the absence of disclosure prevents a full assessment.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
7 researchersIf this is your work, this is how we attribute it on Fit Body Science. Emily W. Miro is listed as the lead author.