A group of researchers in Germany and Sweden recruited 39 competitive male chess players, who had an average IQ of 127 and an average chess Elo rating of about 1700 (an above-average rating in the system used to determine serious players’ skill level). They divided the group to test their performance after consuming either 200 mg of modafinil, 20 mg of ritalin, 200 mg of caffeine, or a placebo.

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