VIENNA – , new research suggests.
In a randomized controlled trial, 40 healthy adults were given the attention-deficit/hyperactivity disorder (ADHD) treatments methylphenidate or dexamphetamine or the wakefulness-promoting drug modafinil vs. placebo.
While receiving the so-called “smart drugs,” participants spent more time and made more moves more quickly while solving each problem on a complex cognitive task than when given the placebo. But with no significant improvement in overall performance, all drugs were associated with a significant reduction in efficiency.
The findings “reinforce the idea that, while the drugs administered were motivational, the resulting increase in effort came at a cost in the loss of productivity,” said study presenter David Coghill, MD, PhD, chair of developmental mental health, the University of Melbourne.
This was especially true for individuals who scored high when receiving placebo, “who ended up producing below average productivity when on the drugs,” he noted.
“Overall, these drugs don’t increase the performance. Instead, they cause a regression to the mean, and appear to have a more negative effect on those who performed best at baseline,” Dr. Coghill added.
He presented the findings at the 35th European College of Neuropsychopharmacology (ECNP) Congress.
Past evidence ambiguous
Dr. Coghill noted that prescription-only stimulant drugs are increasingly used by employees and students as “smart drugs” to enhance workplace or academic productivity.
He conducted the study with colleagues from the department of economics at his institution, because of “their interest in people using cognitive enhancers within the financial industry, in the hope that that would increase their productivity in what is a very competitive industry on the floor of the trading rooms.”
However, while “there’s a subjective belief” that these drugs are effective as cognitive enhancers, the evidence to actually demonstrate that in healthy individuals “is, at best, ambiguous,” he told meeting attendees.
Improvements in cognitive capacities, such as working memory and improved planning, are most evident in clinical populations such as those with ADHD, which could be due to a “ceiling effect” of the cognitive tasks in healthy individuals, Dr. Coghill noted.
To investigate further, the researchers conducted a randomized, double-blinded trial of standard adult doses of methylphenidate (30 mg), dexamphetamine (15 mg), and modafinil (200 mg) vs. placebo. The healthy participants (n = 40), all of whom were aged 18-35 years, crossed to each of the other treatment groups over the course of four intervention sessions.
All were asked to solve eight instances of the knapsack task, the aim of which is to place theoretical objects in a knapsack to achieve the maximum value within a certain weight limit.
“This looks very simple but as the number of items increases, it becomes incredibly complex to compute, and actually is not computable using standard approaches. You have to deal with trial and error,” Dr. Coghill said.
The participants also completed several CANTAB cognitive tasks.