I don’t that on T-mag we’ve said that 4-AD “does” reduce estrogen, but rather that it “does not increase estrogen.” On a couple
of occasions, it’s possible it says it may reduce it, because there’s some indications of that.
The fact that 4-AD increases testosterone levels but not estrogen levels is explainable,
so far as I can imagine, only by 4-AD (like
DHT, Proviron, androstanedione, and some other
steroids) having some binding to aromatase. Since it cannot itself be converted to estrogen – is binding the enzyme and the enzyme can do nothing with it – it’s a blocker or inhibitor. So T levels can go up some, but if aromatase is partially blocked, estrogen levels would not rise.