Consumption of refined sugars in the form of soft drinks is increasingly recognized as a public health concern with major implications for cardiovascular diseases. These adverse consequences might be exacerbated by caffeine, which is often added to soft drinks, particularly in popular "energy" drinks. In young healthy subjects, we tested whether the acute consumption of an energy drink would impact on hemodynamic variables, particularly in elevating blood pressure, and affect cerebral blood flow velocity (measured by transcranial Doppler) and microvascular endothelial function. We also tested whether consuming a popular energy drink would potentiate the cardiovascular responses to a mental stress test. Our results show that consumption of an energy drink increases the workload to the heart and decreases cerebral blood flow velocity. Performing a mental arithmetic task imposes an additional cardiovascular load. Taken together, our data suggest that the acute ingestion of an energy drink results in an unfavourable cardiovascular and cerebrovascular profile, which could affect people suffering from hypertension and cerebrovascular diseases adversely.