The multitude and magnitude of the various negative influences which downgrade endogenous testosterone production may never be known. From the lectures I have attended by Dr. Reiter, re-establishing circadian rythm--and getting proper sleep--trumps all.
The simple and most basic fact is (1) we are ALL quite deficient in melatonin, and (2) we really need melatonin to be healthy.
Yes, administering TRT is definitely seizing control of the HPTA (and very much influencing many other systems as well). That is how we should always look at it.
Dr. Reiter has published over 1,200 papers on melatonin. We indeed know a lot about it. Unfortunately, most of what people think they know is BroScience i.e that melatonin inhibits its own production.
IF it turns out to be true melatonin is also an aromatase inhibitor, all the better.