T decreased in Group 1 from mean 169 ng/dL to 87.4 ng/dL (β48.2%) and in Group 2 from mean 642 ng/dL to 49.2 ng/dL (β92.3%). In the groups combined, T following treatment would be mean 69.8 ng/dL. Per authors, spironolactone was intended to help reduce T and facilitate feminization while MPA was intended to help suppress gonadotropins and T and improve breast development.
When coupled with estradiol, effects in transgender women include decreased male pattern body hair, induction of breast development and of feminization in general, and reduced spontaneous erections.
Canβt find a primary source that explains if/why spiro has feminizing properties when used with E that are not due to the suppression of T (which it does seem really, really bad at lol)