You really have to know (whether or not) if you are prone to acquiring gyno in the first place, and the real only way to know is to start a cycle without it. Then if you are feeling symptoms, i.e. tenderness directly under the nipples, which would be followed by downright soreness, which would then be followed by being able to feel a "lump" or a small "growth" with your fingers, and ultimately a visible enlargement in (usually right below) the nipple. Kind of like Div said, have it as a precaution, but I discovered through my early trial and error days, that you better catch it REAL early, and make sure that you block or inhibit any more estrogen from aromatising. If you don't want to find out whether or not you are gyno-prone, then you better use the anti e, or e blocker from week 2 all of the way through, and even 3 weeks after. IMO I belive that you may be a tad bit weaker with the Anti-E, but on the take side, you do look better because you are dryer.