 As caffeine is mainly used because of perceived stimulant properties, including enhanced mental alertness and increased energy, research has been conducted to examine the effects of caffeine on cognitive performance in humans. These studies have identified beneficial effects of caffeine on a wide-range of cognitive processes including verbal working memory, sustained attention, and executive function. It must be noted, however, that while many studies report pro-cognitive effects of caffeine, others report no significant improvements or deficits in performance. This may be at least partially explained by evidence suggesting an inverted U-shaped dose-response curve for caffeine, wherein lower doses have positive effects on performance, while high doses i.e., above 500 mg cause a decrease in performance. 