NEW YORK (Reuters Health) Jul 07 - Metabolife 356, a best-selling ephedra-containing dietary supplement, can increase heart rate and cause cardiac arrhythmias, according to a report in the June 15th issue of The American Journal of Cardiology.

Ephedra-containing dietary supplements have previously been associated with myocardial infarction, cardiac arrhythmia, hypertension, and death, the authors explain. One such supplement, Metabolife 356, also contains a variety of herbs, including ma huang, guarana, ginger, ginseng, gotu kola, and various vitamins and minerals.

Dr. Stephanie F. Gardner from University of Arkansas for Medical Sciences in Little Rock, and associates used 24-hour Holter monitoring and other methods to evaluate the short-term effects of Metabolife 356 on blood pressure, heart rate, and hemostatic parameters in 10 healthy men.

"We chose day 3 as the time of maximal sympathetic cardiac stimulation and day 14 as the time of tolerance from sympathetic stimulation," the researchers explain.

Mean blood pressures increased after 3 days of treatment (6 mm Hg systolic and 8 mm Hg diastolic), the authors report, but returned to baseline by day 14.

Mean heart rate also increased at day 3, the results indicate, with subjects experiencing significantly fewer bradycardia runs. Heart rates returned to baseline by day 14.

Two men developed large numbers of atrial premature contractions and couplets on day 3, the researchers note, and another subject experienced a 3-beat run of ventricular tachycardia on day 3 of supplementation.

All subjects reported adverse effects at day 3, with dry mouth, shakiness, and insomnia predominating. Dry mouth and shakiness were the most common complaints at day 14.

"Healthy adults taking ephedra-containing dietary supplements should be cautioned regarding the potential for adverse cardiovascular events, especially if these supplements are combined with other cardiovascular stimulants or physical exertion," the authors conclude.

"Because persons with underlying cardiovascular disease are at increased risk for life-threatening arrhythmias and thrombotic events, the use of ephedra-containing dietary supplements should be strongly discouraged."

Am J Cardiol 2003;91:1510-1513.