The drugs are commonly prescribed for Attention Deficit Hyperactivity Disorder (ADHD), but are taken by some people who do not have ADHD because of a belief the drugs will enhance focus and cognitive performance.

In a double-blinded, placebo-controlled trial in Melbourne, 40 healthy participants took one of three popular ‘smart’ drugs (Methylphenidate, Modafinil or Dextroamphetamine), or a placebo, and were tested on how they performed. The test was repeated four times, at least one week apart, to measure how they each performed with the drugs and without (placebo condition).

In general, participants taking the drugs saw small decreases in accuracy and efficiency, along with large increases in time and effort relative to their placebo condition.

In addition, participants who performed at a higher level in a placebo condition compared to the rest of the group tended to exhibit a stronger decrease in performance and productivity after receiving a drug. By contrast, participants who had a lower performance in a placebo condition only very occasionally exhibited a slight improvement after taking a drug.

Professor Peter Bossaerts, Leverhulme International Professor of Neuroeonomics at the Faculty of Economics at the University of Cambridge, said research needs to be conducted to find out what effects the drugs are having on users.

“It was expected, because of the increased dopamine the drugs induce, we would see increased motivation, and a concurrent increase in the chemical norephinephrine would cause an increase in effort, which in turn would lead to higher performance. This did not occur, so questions remain about how the drugs are affecting people’s minds and decision making,” said Professor Bossaerts.

Dr Elizabeth Bowman, researcher at the Centre for Brain, Mind and Markets, University of Melbourne, and lead author of the study, said the results show the effectiveness of pharmaceutical enhancers when used by healthy people in everyday complex tasks has yet to be established.