BackgroundCaffeine in doses <400 mg is typically not considered arrhythmogenic, but little is known about the additional ingredients in energy drinks. We evaluated the ECG and blood pressure (BP) effects of high‐volume energy drink consumption compared with caffeine alone.Methods and ResultsThis was a randomized, double‐blind, controlled, crossover study in 18 young, healthy volunteers. Participants consumed either 946 mL (32 ounces) of energy drink or caffeinated control drink, both of which contained 320 mg of caffeine, separated by a 6‐day washout period. ECG, peripheral BP, and central BP measurements were obtained at baseline and 1, 2, 4, 6, and 24 hours post study drink consumption. The time‐matched, baseline‐adjusted changes were compared. The change in corrected QT interval from baseline in the energy drink arm was significantly higher than the caffeine arm at 2 hours (0.44±18.4 ms versus −10.4±14.8 ms, respectively; P=0.02). The QTc changes were not different at other time points. While both the energy drink and caffeine arms raised systolic BP in a similar fashion initially, the systolic BP was significantly higher at 6 hours when compared with the caffeine arm (4.72±4.67 mm Hg versus 0.83±6.09 mm Hg, respectively; P=0.01). Heart rate, diastolic BP, central systolic BP, and central diastolic BP showed no evidence of a difference between groups at any time point. Post energy drink, augmentation index was lower at 6 hours.ConclusionsThe corrected QT interval and systolic BP were significantly higher post high‐volume energy drink consumption when compared with caffeine alone. Larger clinical trials validating these findings and evaluation of noncaffeine ingredients within energy drinks are warranted.Clinical Trial RegistrationURL: http://www.clinicaltrials.gov. Unique identifier: NCT02023723.