Research supports a shift toward estradiol monotherapy for trans women, using estradiol alone without additional testosterone blockers.

A groundbreaking study published in the Journal of the Endocrine Society reveals that injectable estradiol may significantly improve hormone therapy outcomes for trans women, Pink News reports.

Researchers analyzed data from 29 patients who switched from traditional estradiol forms (gels or tablets) to weekly injections over a 15-month period. Despite receiving a lower average dose (3.7 mg vs. 4.3 mg), all participants experienced a dramatic reduction in testosterone levels, while maintaining stable estrogen levels.

The study also challenges the efficacy of Spironolactone, a commonly prescribed anti-androgen.

From the research paper Injectable Estradiol Dosing Regimens in Transgender and Nonbinary Adults Listed as Male at Birth: Results The average estradiol dose decreased from 4.3 to 3.7 mg weekly (P < .001) during the study period with a final on-treatment estradiol level of 248 pg/mL. All individuals achieved a testosterone level of less than 50 ng/dL during the study period. The average initial on-treatment testosterone level was not significantly different from average final on-treatment measurement of 24.0 mg/dL (P = .95). Spironolactone use at study initiation was not associated with a lower initial on-treatment testosterone level, though it was associated with a lower estradiol level of 285 pg/dL compared to 427 pg/dL for those on estradiol monotherapy (P = .017). Conclusion Lower doses of injectable estradiol can achieve therapeutic estradiol levels with excellent testosterone suppression. Spironolactone was not associated with additional testosterone suppression and may result in lower estradiol levels.