It will probably help you work with a hightened intensity, but it will probably also help you get rid of calories - which means you'd have to eat just a little more.
Try them and see what happens...You probably don't have to worry about them ruining your cycle or anything, but be careful when you're playing with ephedrine if you don't know if you can handle it or not. I'm in the little group of people who can take a double dose of ephedrine hcl and go back to sleep, while other people will get the jitters from seeing a box of sudafed in a shop window.