A variety of physiological and psychological effects attributed to energy drinks and/or their ingredients have been investigated.
Significant improvements have been reported in mental and cognitive performances as well as increased subjective alertness. Excess consumption of energy drinks may induce mild to moderate euphoria primarily caused by stimulant properties of caffeine and may also induce agitation, anxiety, irritability and insomnia. In young healthy adults an energy drink significantly increased upper body muscle endurance. It was also suggested that reversal of caffeine withdrawal is a major component of the effects of caffeine on mood and performance.
Restorative properties were shown by a combination of caffeine and the sugar glucose in an energy drinks, and some degree of synergy between the cognition-modulating effects of glucose and caffeine was also suggested.