I went down a little late night rabbit hole on Mast and just started looking at my bloods since I started to feel like there's alot of oversimplification on how many say things. Here's a quote of a guy that has a few papers on Mast when asked about if it drys or out or just bro science
Yes, it does this by preventing estrogen uptake into cells. This is not SERM-like action, but more analogous to Epistane action, where tissue-level estrogen modulation occurs (SERMs act antagonistically at the estrogen receptors in the hypothalamus and pituitary). As a brief tangent, Epistane's non-methylated counterpart (epitiostanol) is used clinically in Japan. At a 20 mg weekly dosage epitiostanol, considered an anti-estrogen agent, it was shown to be more effective than Masteron (at 50 mg weekly) in treatment of gynecomastia.
I can link his work if cared.
It definitely drys you out. This can be a very good or bad thing, depending on how dry you want to be (heavy training for strength or growth certainly isn’t the same scenario as a bodybuilder very close to stage time).
I am using the term SERM VERY loosely. My goal is not to explain the exact mechanism, which I do not claim to know. Simply that bloods from guys using Mast tend to have higher estrogen levels than when using Primo, but still won’t have gyno issues, be just as dry or dryer, and can have higher libido.
Many people find test/primo can be a 1:1 with blast level doses, but find Masteron to be drier and need less mg for that level of drying. For example, at cruise using 180mg of test e/wk, I could tolerate 120mg primo. It felt a bit dry, but I was able to tolerate it. On the same 180 test/wk next cruise, 100 mast was to immediately too much, and 80 mast/wk eventually had my joints aching and I suffered an adductor tear eventually.
Part of it was I was leaner the second cruise, therefore aromatizing less, BUT from cycles I have done I find Mast to be more potent in reducing estrogen symptoms/practical effects per mg than primo.
Not to say primo is weak in that action - I took about 450mg of primo e/wk last December and within a week or so it allowed me to take 20mg of Trest Ace daily with no AI. I eventually worked up to 30mg Trest/day along with 20mg IM Dbol. As long as I took my 200mg of P5P and DIM, I was good.