Testosterone therapy is not associated with a rise in oestrogen levels among transgender men, according to a new study led by Boston Medical Center (BMC). In fact, the researchers observed an initial decline in oestrogen levels, which later stabilised and remained within the normal range during the study’s six-year period. The results support that there are no additional risks to female reproductive tissues during testosterone therapy in transgender men.

Current treatment guidelines for transgender men using testosterone therapy suggest that there is a potential need for estrogen lowering strategies, including the removal of the uterus or ovaries, to lower the reproductive health risks. Higher estrogen levels have been shown to be a risk factor for endometrial cancer, pelvic pain, and other health complications. This study suggests that oestrogen reducing strategies may not be necessary, and testosterone therapy alone can be a safe and effective treatment for transgender men.

The study followed the health of 24 transgender men over six years who were treated with testosterone therapy at Boston Medical Center. Researchers checked participants’ oestrogen and testosterone levels every three months for the first year of the study, and every six months for the following years. Most of the patients were starting testosterone therapy at the beginning of the study, and researchers were able to compare their baseline oestrogen levels to those seen throughout treatment.

The study is the first to demonstrate how oestrogen levels respond to testosterone treatment in transgender men over an extended period of time. Future research should observe these trends among a larger sample of participants.

"There are no nationally representative data sets to prove the efficacy of hormone therapy," said Dr Joshua Safer, former medical director of the Center for Transgender Medicine and Surgery at BMC. "Clinic-based studies like this can inform best-practice recommendations and help transgender men feel confident in the safety of their care."

The study has been published online in Endocrine Practice.