nuh_mizer, I almost just flamed you.. but, what the hell, I guess I'm really not like that.
Ephedra (proper spelling) is an herbal extract standardized to produce a certain amount of Ephedrine in your body; usually at 8%. Therefore, most of the thermogenic stacks you'll find will have somewhere around 300mg of Ephedra, producing approximately 24mg Ephedrine.
Ephedrine (proper spelling) is a bronchial dilator, that once introduced to your bloodstream, will increase the amount of oxygen you are able to take in and process.
-B