Some studies show that energy drinks can reduce feelings of sleepiness and fatigue,[1][2][3] increase feelings of alertness,[4][5] and improve some aspects of cognitive function, including mood,[4] attention,[6][7][4] memory,[8][6][4] and reaction time.[9][10][11][5] Energy drinks have also been shown to reduce ratings of perceived exertion (RPE) during exercise and enhance aerobic and anaerobic exercise performance.[9][12][13][14] However, existing randomized controlled trials examining the effects of energy drinks are few in number, include small numbers of participants, and often lack a control group for each ingredient. Furthermore, existing trials have large variability in the types of participants, testing modalities, and product ingredients. Therefore, further high-quality research is needed to make firm conclusions.
It is also important to note that caffeine is the primary ingredient — and typically the sole stimulant — added to energy drinks.[9][15] Consequently, it is very likely that caffeine is responsible for the above-described effects of energy drinks because ample evidence shows that all of these effects are also caused by caffeine in isolation.