Context Metabolife 356, a multicomponent dietary supplement containing ephedra
and caffeine (DSEC) in addition to several other components, is the top-selling
dietary weight loss supplement. Given its common use, anecdotal reports of
cardiovascular and cerebrovascular adverse events, and paucity of safety data,
further research with this DSEC was warranted.
Objective To determine the impact of the DSEC on corrected QT (QTc) interval duration
and systolic blood pressure (SBP).
Design Randomized, double-blind, placebo-controlled, crossover study conducted
from January to May 2003.
Setting and Participants Fifteen healthy volunteers (mean [SD] age, 26.7 [2.52] years; weight,
72.7 [14.93] kg), 6 (40%) of whom were women, recruited from the University
of Connecticut, Storrs campus.
Intervention A single dose of the DSEC (containing 19 ingredients including ephedra
[12 mg] and caffeine [40 mg]) or matching placebo were administered in a crossover
fashion with a 7-day washout period between treatments.
Main Outcome Measures Maximal QTc interval and SBP assessed at 1, 3, and 5 hours after dosing
for the DSEC relative to placebo.
Results Individuals receiving the DSEC had a longer maximal QTc interval (mean
[SD], 419.4 [11.8] vs 396.1 [15.7] milliseconds; P<.001)
and higher SBP (mean [SD], 123.5 [10.98] vs 118.93 [9.62] mm Hg; P = .009) compared with placebo. Participants who received the DSEC
were more likely to experience a QTc interval increase of at least 30 milliseconds
vs placebo (8 individuals [53.3%] vs 1 individual [6.7%]; relative risk, 2.67
[95% confidence interval, 1.40-5.10]). There were no significant sex-related
Conclusions The ephedra- and caffeine-containing dietary supplement Metabolife 356
increased the mean maximal QTc interval and SBP. Since the actual ingredient
or ingredients in Metabolife 356 responsible for these findings are not known,
patients should be instructed to avoid this and similar dietary supplements
until more information is known about their safety.