I was envisioning an experiment in which men would be given something like lilopristone, a PR antagonist, to see if anything bad happens. But you really need something that irreversibly binds to progesterone itself and effectively deactivates it. Then one would also be testing whether progesterone's opposition to estradiol is important.
I wouldn't be so quick to dismiss the importance of allopregnanolone. Wiki cites this reference in saying that it is "prosexual". There is some discussion of human studies also.
Our research has demonstrated that 3α,5α-THP facilitates social and sexual behavior of rodents, which evokes further increases in 3α,5α-THP in midbrain and hippocampus, brain areas involved in [social, cognitive, emotional and physical processes].
The drop in progesterone under TRT may be small in absolute terms, but losing half of the total seems significant. How is that unlikely to have biological consequences? Try losing half of your testosterone or estradiol. I also see that the lead author of the study received some perks from Bayer, which could be an incentive to downplay the issue.
