Introduction: Gender dysphoria refers to the incongruence between the subjects experienced sex on the one hand and the assigned sex on the other hand. Several studies assume a relationship between oestrogen substitution therapy and serum prolactin levels.
Aim: The aim of this study is to get more insight into the effect and time-course of changes in serum prolactin levels during cross-sex hormone therapy.
Methods: This prospective study included 82 transgender persons who completed 1 year of treatment, 45 male-to-female individuals (MtFs) (mean age±S.D. 34±13 years) and 37 female-to-male individuals (FtMs) (mean age±S.D. 27±10 years). MtFs were treated with cyproteronacetate (50 mg/day) and estradiol valerate (24 mg/day) or an estradiol patch (200 μg/week). FtMs were treated with testosterone esters i.m. (250 mg/2 weeks), testosterone undecanoate i.m. (1000 mg/12 weeks), or testosterone gel (50 mg/day). We determined serum prolactin levels at baseline and after 3 and 12 months. Serum prolactin was measured by immunometric assay (Centaur, Siemens).
Results: In MtFs mean serum prolactin levels increased from 0.16 to 0.41 U/l (160% (132188%)) between 0 and 3 months and from 0.41 to 0.47 U/l (15% (0.229%)) between 3 and 12 months (mean level in biological women 0.28 U/l). In FtMs mean serum prolactin levels decreased from 0.27 to 0.23 U/l (−16% (−28 to −4%)) between 0 and 3 months and from 0.23 to 0.21 U/l (−9% (−30 to 13%)) between 3 and 12 months (mean level in biological men 0.16 U/l).
Conclusions: In MtFs an increase in mean serum prolactin levels was seen whereby those levels exceeded mean serum prolactin levels of biological women. In FtMs a decrease in mean serum prolactin levels was seen whereby those levels did not reach the values of biological men. In both groups the biggest change was observed during the first 3 months of treatment.