What's in Speed Stack? Zero sugar, 5 calories, and one measly little carb. Oh, and then there's 250 milligrams of caffeine, plus a 960 milligram MethXanth Stack packed with DMAE, Guarana, Yerba Mate, Theobromine, Synephrine, Octopamine, and just about any other "ine" you'd want before your next workout or competition. This is one serious liquid power stack.