Supplements that contain ephedra and caffeine-rich guarana, which may be used for weight loss, result in significant cardiovascular and metabolic changes, investigators have found. These changes could be harmful in people with high blood pressure, atherosclerosis (clogged arteries), or glucose intolerance, a precursor to diabetes marked by elevated blood sugar. All of these conditions are strongly associated with obesity. Even though the US Food and Drug Administration banned ephedra as a dietary supplement for weight loss, it is still obtainable as a traditional Chinese medicine, ma huang, the authors note in the journal Clinical Pharmacology and Therapeutics. Synthetic ephedrine is also available in convenience stores and over the Internet. Guarana is an herb containing caffeine. Dr. Christine A. Haller and her colleagues at the University of California, San Francisco tested the effects of Xenadrine RFA (a multi-component supplement containing 25.4 mg ephedra alkaloids and 185 mg caffeine) and ephedra extract (23.2 mg total ephedra alkaloids) plus guarana (167 mg caffeine), compared with placebo, in 16 healthy adults. They report that repeated dosing of ephedra and guarana produced elevated ephedrine blood concentrations, increased heart rate and blood pressure, and had unfavorable effects on glucose and potassium homeostasis. These effects could exacerbate obesity-related conditions such as insulin resistance and metabolic syndrome, the authors note. Linky.... http://www.nlm.nih.gov/medlineplus/news/fullstory_25697.html It really seems you can't win.