“Those who’d scored above average after taking the placebo tended to fall below average while on one of the drugs.”
Forty healthy adults took Ritalin, modafinil, dextroamphetamine or a placebo and solved knapsack problems. The drugs made them work longer and shuffle more items in and out. Their productivity dropped under all three. Students popping stimulants before exams are buying the feeling of effort, not the result.