There are differences in Rx grade GH. I've used Humatrope, Serostim, Genotropin, Nutropin AQ, and Omnitrope. Humatrope is my favorite, and seems to keep me noticeably fuller than the others. I also feel like I can sleep all day on it. Serostim stimulates my appetite more than the others, and the Genos seem to hold the least amount of water out of any of them, although the water retention with any of the Rx GH is minimal. The differences are not big, but there are subtle differences in different brands of GH. You just have to try them and see which one you like best. I use Serostim and Humatrope all the time, but you can't go wrong with any Rx GH. The only downside is that they all make me quite tired.