depends what you're looking at. if the product contains ephedra leaves, then it's what you call a "knock off". it's a scam, it doesn't work. Yes! phedra is in there, but the leaves are inactive for burning fat. the key words you are looking for are "alkaloids", "ephedrine HCl", and "ephredrine sulfate."
most ephedrine alkaloid-based fat burners are off the market since (i believe) they are currently banned. anything that's marketed as a fat burner with ephedra is banned. some places have it on the shelves cause some guy bought the entire stock from the factory of, hmm... lipodrene I believe. and now he's selling it to stores. they won't get any more of the real stuff nowadays, from here on out all the stores online and retail are just leaving the fat burners on the shelves until they are all sold out.
want the real goods, legally? go to rite aid or a local drug store and pick up some bronkaid. it's got 25mg of ephedra sulfate in there and it's legit. just tell the pharmacist that it's for your asthma ;-) there's no sign of it being banned or discontinued as of yet.