I just finished my second marathon using Tailwind. I ran my first marathon with a hydration pack and tailwind was the only thing I used the whole 26 miles. No GI issues and the only fuel I needed. This 2nd marathon we were not able to run with hydration packs, so I saturated my bottles with tailwind and picked up water along the way. Once again this was all I needed and I had no problems with my stomach. I have tried many other options and have always ended up with extreme stomach aches. I personally like all the flavors. But my go to combo is green tea and lemon.