Effectiveness and Safety of Different Estradiol Regimens in Transgender Females: A Randomized Controlled Trial

Background: A goal of gender-affirming hormone therapy (GAHT) for transgender women is to use estradiol to suppress endogenous production of testosterone. However, the effects of different estradiol regimens and route of administration on testosterone suppression is unknown. This is the first open-label randomized trial comparing different GAHT regimens for optimal estradiol route and dosing. Objective: To evaluate 1 month and 6 months testosterone suppression <50 ng/dL with pulsed (once- or twice-daily sublingual 17-beta estradiol) and continuous (transdermal 17-beta estradiol) GAHT. Methods: This study was conducted at an outpatient adult transgender clinic. Thirty-nine transgender women undergoing initiation of GAHT were randomly assigned to receive either once-daily sublingual, twice-daily sublingual, or transdermal 17-beta estradiol. All participants received spironolactone as an antiandrogen. Doses were titrated at monthly intervals to achieve total testosterone suppression <50 ng/dL. Results: Transdermal 17-beta estradiol resulted in more rapid suppression of total testosterone, lower estrone levels, with no differences in estradiol levels when compared to once-daily and twice-daily sublingual estradiol. Moreover, there was no difference in the mean estradiol dose between the once-daily and twice-daily sublingual 17-beta estradiol group. Conclusion: Continuous exposure with transdermal 17-beta estradiol suppressed testosterone production more effectively and with lower overall estradiol doses relative to once or twice daily sublingual estradiol. Most transgender women achieved cisgender women testosterone levels within 2 months on 1 or 2 0.1 mg/24 hours estradiol patches. Given no difference between once- or twice-daily sublingual estradiol, pulsed 17-beta estradiol likely provides no benefit for testosterone suppression.