"A group of 39 highly rated male members of the German Chess Federation were enlisted to play more than 3000 15-minute games against computers matched to their skill levels while taking modafinil, methylphenidate, or caffeine. The researchers reported that players taking modafinil and methylphenidate won more games overall, though they pondered their moves longer, causing them to sometimes lose on time.""The positive association surprised Lieb. “Our hypothesis [had been] that it’s not possible to enhance subjects who are already working at top performance,” he said."
Lyon J. Chess Study Revives Debate Over Cognition-Enhancing Drugs. JAMA. Published online August 16, 2017. doi:10.1001/jama.2017.8114