In this work, we evaluate the effect of having energy drinks (ED) using laser doppler flowmetry (LDF) technique by analyzing blood perfusion and ECG signal after having energy drinks on different healthy human subjects. After having energy drinks, it is observed that the amplitude of blood perfusion signal increases around two fold. Further analyzing frequency spectrum of the blood perfusion signal using Fast Fourier transform, we have determined the effect of having energy drinks on respiratory and heart function. A significant change in heart activity after having energy drinks has been observed. The amplitude of frequency spectrum of LDF signal related to heart activity increase around three fold. The amplitude of ECG signal and amplitude of frequency spectrum also increase in response to having energy drinks. A little change is observed in respiratory activity as the amplitude of frequency spectrum of LDF signal corresponding to respiratory activity increases around 1.5 times after having energy drinks.