letro will stop all estrogen dead! but post stats, history, and cycle so we can get an idea if your on anything else.. because honestly, 300mg shouldnt do jack unless your just FREAKISHLY prone to gyno...? never know...? but your sure your not on something more... letrozale is the most direct and strait way to go, i dont know why those people up there said nolva and clomid wont work, it will, but nolva more less takes care of the sides arimidex and letrazole go after the culprit, estrogen in its receptors, they will bind to it and make it spot producing all thogether,(letro being stronger), but clomid and nolva will keep it under control...but if its deca remeber it stays active for several weeks that means even if it goes away while on nolva or clomid... if you stop taking them, estrogen levels will go right back up! and gyno will come right back even if your last shot was 3weeks previous, so youll have to take them until the ester is outa your blood stream... might be a while... luck man...