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Decision making, Education

Smart drugs aren’t so smart after all

New study finds that so-called ‘smart drugs’ reduce the quality of effort, and increase time taken to complete a decision-making task in cognitively healthy people.

09 November 2023

By Emma Young

According to previous research, most university students think it's normal to use drugs prescribed for conditions such as ADHD and narcolepsy as 'cognitive enhancers'. Many students have few qualms taking a dose with the aim of improving focus and academic performance.  

For those that use these medications to manage a condition, they can be life changing. However, a recent study in Science Advances has found that for cognitively healthy people, several 'smart drugs' aren't so smart after all. 

Elizabeth Bowman at the University of Melbourne and colleagues studied 40 healthy people aged between 18 and 35. On four test days, held at least a week apart, these participants were presented with eight versions of a problem known as the knapsack optimisation problem, or knapsack task, which is designed to mimic the kind of complex decision-making and problem-solving challenges that we face in daily life. 

The knapsack task involved presenting the participant with a virtual empty bag with a weight limit, along with 10 to 12 different items of different values and weights that could be placed inside. To succeed at the task, the participants had to pack the bag with the combination of items totalling the greatest possible value, while staying under the weight limit. While they worked on this, they were shown the cumulative weight and value of their selected items, but had to complete their packing within a four-minute time limit. By varying the values, weights and number of items, as well as the weight limit, the researchers were able to vary the difficulty level of each individual challenge. 

On each test day, the participants were also given a different identical-looking white pill. One contained a dose of methylphenidate (aka Ritalin, a stimulant used to treat ADHD), one a dose of modafinil (used to treat narcolepsy), and one a dose of dextroamphetamine (another stimulant used for ADHD). The final pill was a placebo. All of three drugs are known to increase levels of dopamine as well as noradrenaline. The team expected that the increased dopamine would boost the participants' level of motivation to complete the task and, with the increased noradrenaline, raise their effort levels, leading to a better performance. 

The results showed that on average, the drugs didn't affect the chance of a participant finding the solution to a knapsack problem. Contrary to perhaps many students' expectations, however, participants tended to perform worse after taking one of the drugs, packing a lower total value of items. 

Not only that, but they spent substantially more time working on their solution while on the smart drugs than they did after taking the placebo. In fact, participants spent almost as much time on the easiest presentations of the knapsack task while on methylphenidate (Ritalin) as they did on the hardest instances of the task after taking the placebo, without any corresponding improvement in performance. 

All of the drugs also increased the number of times the participants moved items in and out of the knapsack. "Thus, if one measures motivation in terms of time spent or number of items moved, drugs clearly enhanced motivation," the team writes. However, on average, the drugs did not increase 'effort quality' or productivity, measured as the average gain in knapsack value per move. Productivity was lower in all three drug conditions, compared with placebo. 

Looking at performances on a group level, though, masks what the team referred to as a "disturbing reversal" in individual performances. Those who'd scored above average after taking the placebo tended to fall below average while on one of the drugs. While on a drug, participants made a poorer, more random first attempt at filling a knapsack than they did after taking the placebo, and this had an especially negative impact on the subsequent performance of those who'd been above average in the placebo condition, explaining why they dropped below the mean. Overall, the results suggest that the participants' approach to solving the knapsack task became less systematic while they were on each of the three drugs, the researchers write.

The results have clear implications: healthy people who take these drugs hoping for cognitive gains may work harder and longer at a problem, but without any benefit. For people who are already pretty good at solving complex problems that require systematic thought — likely many university students — these drugs could even be detrimental. More work will be needed to establish exactly why these drugs have these effects in those without a medical need for them, as well as to explore the potential impacts of other so-called smart drugs. 

Read the paper in full: