San Francisco: The banned diet supplement ephedra is still being bought by consumers. And experts warn that it can cause dangerous changes to the heart.

According to an article in Clinical Pharmacology and Therapeutics these changes, including increased heart rate, could be harmful in people with high blood pressure, atherosclerosis (clogged arteries), or glucose intolerance, both of which are stronglylinked to 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. Synthetic ephedrine is also available in convenience stores and over the Internet, along with guarana, a 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.

This study, they conclude, provides further evidence that dietary supplements containing ephedra and guarana or like-compounds could have unfavorable cardiovascular effects, especially in susceptible individuals such as those with high blood pressure, glucose intolerance or hardening of the arteries.