Estrogen Monotherapy (E Alone)
What Is Monotherapy?
Estrogen monotherapy means using estradiol alone to suppress testosterone, without adding an anti-androgen (spironolactone, bicalutamide, CPA, etc.). The goal is to keep E2 levels high enough that the HPG axis naturally reduces LH/FSH and therefore testosterone production.
How It Works
- High levels of estradiol in the bloodstream signal the hypothalamus/pituitary that there is enough sex hormone
- The pituitary reduces LH and FSH output
- The testes receive less LH stimulation
- Testosterone production decreases
This is the same negative-feedback mechanism that regulates hormone production in cisgender people.
Who Can Use Monotherapy?
Monotherapy is not effective for everyone. Success depends on:
- Route — injectable or high-dose transdermal estradiol works best; oral monotherapy is not recommended
- Individual biology — some people's HPG axes are more sensitive to E2 feedback than others
- Dose — sufficient E2 levels must be maintained at trough
Dosing for Monotherapy
| Route | Dose | Typical Trough E2 |
|---|---|---|
| EV injections | 4–8 mg every 5 days | 200–300 pg/mL |
| EEn injections | 4–8 mg every 7 days | 200–300 pg/mL |
| EC injections | 3–6 mg every 7 days | 200–300 pg/mL |
| Transdermal patches | 200–300 mcg/24h | 150–250 pg/mL |
| Gel | 6–8 pumps/day | 150–250 pg/mL |
Recent clinical evidence (multiple 2024-2025 cohort studies) shows that most people achieve T suppression at the lower end of these ranges. Median effective weekly doses are around 4 mg (IQR 3-6 mg). Starting at 3-5 mg weekly and titrating up if needed is recommended to avoid supraphysiologic E2 levels.
Do NOT attempt monotherapy with oral pills
Oral estradiol at doses high enough to suppress T carries a significantly elevated VTE (blood clot) risk due to first-pass liver metabolism. Monotherapy should only be attempted with injectable or high-dose transdermal estradiol.
Effectiveness
- ~80% or more of trans women achieve T < 50 ng/dL on injectable monotherapy (based on recent cohort studies†)
- Some still need a low-dose anti-androgen even with adequate E2
- People with higher baseline T may need higher E2 doses
- Some studies suggest spironolactone may not provide additional T suppression when combined with injectable E2, though it can still be useful for blocking androgen receptors†
† These findings come from recent observational cohorts (2024–2025). Specific citations were not included as the evidence continues to evolve; readers should consult the latest literature or community evidence summaries for current data.
Pros & Cons
| Pros | Cons |
|---|---|
| No anti-androgen side effects | High E2 doses needed |
| No spiro (potassium, urination) | May not work for everyone |
| No CPA (depression, meningioma risk) | Requires injections (typically) |
| No bica (liver monitoring) | More expensive (higher E2 dose) |
| Simpler regimen | Some people feel worse on very high E2 |
| No anti-androgen cost |
Monitoring
| Test | Target | Frequency |
|---|---|---|
| E2 (trough) | 200–300 pg/mL (for monotherapy) | Every 3 months |
| T (trough) | < 50 ng/dL | Every 3 months |
| SHBG | < 150 nmol/L (may indicate too high E2) | Every 6 months |
| Blood pressure | Normal | Every visit |
Trough timing
For monotherapy, measuring E2 at trough (just before next injection) is critical. Peak E2 levels can be 500–1000+ pg/mL, which is fine — the concern is whether your trough is high enough to suppress T.
When to Add an Anti-Androgen
Consider adding a low-dose anti-androgen if:
- T > 50 ng/dL after 8–12 weeks on high-dose monotherapy
- SHBG is very high (>150 nmol/L) suggesting E2 dose can't go higher
- You cannot tolerate high E2 doses (mood effects, etc.)
- You are on a route that cannot achieve monotherapy-level E2 (pills, low-dose gel)
References
UCSF Transgender Care. Anti-androgens and monotherapy. https://transcare.ucsf.edu/guidelines
Hembree WC, et al. (2017). Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons. JCEM. https://academic.oup.com/jcem/article/102/11/3869/4157558