Stacker 2's are the best bang for the buck. One Stacker 2 contains 25mg of ephedrine. It takes 2 Xenadrines to equal that amount. If you are sensitive to the effects of eph. of caffeine, then go with the Xen. b/c you can only take one. If you're a real man, then pop 2 (or more Stacker 2's) on an empty stomach and have fun bouncing off the walls.