Anectotally, there seems to be some truth to guys having test results that shower lower E2 from cycles with mast over just test. However, what the cause of this is is anyone's guess, and it is not going to be like this for everyone. My guess is guys are getting tested using varying degrees of test, mast, and AIs, and just mixing shit up and confusing their own results. But I wouldn't push that as certain. On the other hand, these guys will straight up tell you that "studies" point to drostanolone specifically having these machanisms of action, and that is just false. There's nothing stopping scientists from putting in their discussion that it appears mast acts this way. Regardless of whether a proper study has even been done to analyze this, bottom line is that data just ain't there. If I'm wrong and someone posts the study, I'll eat my shorts.