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.