DIM (Diindolylmethane) and Calcium D-Glucarate both help with estrogen but you need doses that are a lot higher than whats recommended on the bottle by manufacturer.
I'm not sure if GNC carry's this or not I got mine from vitamin shoppe so I'm assuming GNC should have something about the same or maybe carry's it if not check with vitamin shoppe tell them you want DIM-plus(diindolylmethane)It helped me with slight puffy-ness.
I have not been in GNC for years because everything they ever sold me never did what it claimed to do. If you want good estrogen control go with forma stanzol from mrsupps.com. It is amazing stuff.
Not necessarily. Many OTC supps if consumed in right doses can be a great aid and sourced failry cheap. They also tend to have a lot fewer sides than the real AI and dont F up you HPTA.