I've never used it myself but I've heard mixed reviews some people saying that they had crazy endurance and other people say that they didn't get anything from it. I'm sure that's based on the quality of the GW. I've also heard a really scary story of a guy who said that he took it and now his body won't stop producing excessive amounts of red blood cell's and now he has to give blood as often as he can. The guy is a vet and said that he's done everything in the books but after the GW is when it started happening