Addition of testosterone to endocrine care for transgender women: a dose-finding and feasibility trial.

Objective: Transgender women who underwent gonadectomy have lower serum testosterone concentrations than cisgender women. There is uncertainty regarding the dosing and side effects of supplementation of testosterone in transgender women. This study aimed to assess the feasibility of dosing testosterone to the cisgender female physiological range in transgender women. In addition, we explored changes in cardiovascular parameters, virilizing side effects, and clinical symptoms.

Design: This is an open-label, single-arm feasibility study. Participants initially went through a dose-titration phase with 2-week intervals of 0.07-0.09-0.13 mL (277-318-403 μg bioavailable testosterone) testosterone 2% gel to establish a dose leading to serum testosterone concentrations between 1.5 and 2.5 nmol/L. This dose was then continued for 8 weeks.

Methods: Participants applied daily transdermal testosterone 2% gel (Tostran®) at the prescribed dosage. Testosterone was measured every 2-4 weeks. Laboratory analyses, side effects, and clinical symptoms were evaluated.

Results: In total, 12 participants were included. Most participants required a dose of 0.07 mL (277 μg bioavailable testosterone) or 0.09 mL (318 μg bioavailable testosterone) to reach serum testosterone concentrations of 1.5-2.5 nmol/L. Continuing this dose, testosterone concentrations remained stable throughout the study. Changes in clinical outcomes were in the desired direction, and side effects were mild.

Conclusions: The use of testosterone supplementation in transgender women seems feasible and safe in the short term. Although dosing requires personalized titration, stable testosterone levels can be established. A blinded, placebo-controlled, randomized clinical trial is needed to study the clinical benefit.