I take both ECA (and a cup or two of coffee on top of that) and I take creatine. I have had the benefits of both with no problems. The main conflict bw caffeine and creatine is that creatine helps your muscles store water (with creatine/glycogen etc), and caffeine is a diuretic. If you drink plenty of water- which you should be doing anyway- you should have no problems. ALTHOUGH! I recommend not starting caffeine if you don't already. It is not a good habit. I am an addict, decided not to bother quitting until my body fat gets low enough. If you don't take caffeine yet- don't start, getting enough sleep will keep you from being tired, and creatine will help lift those heavy weights!