Background: Many studies on the cardiovascular complications linked to energy drinks consumption imply that their effect on endothelial function might be a causal factor in subsequent cardiac events. Aim: This research investigated whether energy drinks consumption could cause acute endothelial function impairment as surrogated by flow-mediated dilation in healthy young adults. Subjects and methods: This observational study was done in Benha University Hospital in the period from July 2021 to June 2022, and included 50 healthy young adults for analyzing the normal endothelial function before and after consuming a single popular energy drink (ED) can, to assess its effect on endothelial function. All subjects underwent full history taking, clinical examination, Electrocardiogram, and flow-mediated vasodilation (FMD) measurements.