Let me try to make some points.
1. Ephedra and ephedrine are not the same thing. Ephedra is just a name for a mixture of ephedrine like compounds that may or may not even contain 1 molecule of ephedrine. Even if a product says it's "standardized", you should check what it's standardized to. For example, St. John's Wort is almost always standardized to hypericin while hyperforin is the actual compund that is alleged to affect depression/mood (although neither has been shown to work).
Thus, ephedra DOES NOT do anything. You have to find someone who has real ephedrine. In my state as well as many others, however, ephedrine (although not ephedra) is a C-IV )like Valium and Xanax) making it difficult to come across. But ephedrine has shown for so many years to be effective in short term weight loss (although few compounds have shown efficacy for over a year despite cycling).
2. Is ephedra harmful? Yes and no. If you have diabetes or high blood pressure or heart disease, ephedrine is not recommended, Why? Just like Rhapsody said, you are vasoconstricting and causing raising in blood pressure and restricting oxygen to those that are already restricted to several areas (such as in diabetic extremeties and hearts or in people with heart disease). The water hose example she gave is perfect. Think about it. Also, what happens if you have old blood vessels (analogous to the old hose)? Well the hose can break and blood willl spill internally causing a massive stroke or a blood clot that could easily lead to death. So, if you have these and other disease states, ephedrine is not worth the risk.
3. Ephedrine has 4 isomers. Isomers are compunds that are like your right and left hands. They look similar but they're mirror images. Two of the isomers do something in your body. Two do not. There is one that stimulates beta receptors directly. However, epheda binds weakly and doesn't stimulate well. It's best part is the isomer that stimulates norepinephrine (nor-Adrenaline) release. Thus, this seems to be the most effect. Unfortunately, the weak ephedrine that actually binds to the beta receptors is actually blocking the stronger norepinephrine getting to the beta receptor. So, you're not getting as good of a response as a pure beta agonist like clen.
A weak compound blocking a strong one? This may not make sense at first but it goes a little something like this ... If you see a hot girl at the bar and some slimy little guy is hitting on her, you have to wait until she "dismisses" him until you get yoour chance. Now a lot of your night is gone and wasted due to this other guy. Similarly ephedrine wastes norepinephrine's time by sitting at the beta receptor (the girl) for a while until it is broken down by compounds that get rid of things at the receptor level (the bouncers at closing time). (How male chauvinistic eh Rhap?)
Also, smoking has much more than vasoconstrictive properties that make it bad for you/ But that's for another post.
