(NewsNation) — Stimulants like Adderall can help those with Attention Deficit Hyperactivity Disorder with their focus and cognitive performance — but they could actually have the opposite effect on those without it.

These prescription-only pills are increasingly used by some employees and students as “smart drugs” to become more productive even if they do not have a diagnosis, researchers wrote in the study, which was published in ScienceAdvances.

Researchers conducted four double-blinded, randomized trials in Melbourne, Australia, each a week apart, where 40 participants took one of three drugs commonly used for ADHD or a placebo. These 40 people were then tested in an exercise called the Knapsack Optimization Problem, where they were given a virtual bag with a set capacity, and a selection of items with different weights or values.

Participants were tasked with how best to fit the items into the bag to maximize the overall value of its contents. Overall, those who took the actual drugs saw small decreases in accuracy and efficiency — and large increases in time and effort taken.

According to the news release, participants given the drug methylphenidate took about 50% longer on average to complete the Knapsack Optimization Problem.

Study author and University of Cambridge Professor Peter Bossaerts said in a statement that more research on the effects of ADHD medication on those who don’t have the disorder is needed.

“Our results suggest that these drugs don’t actually make you ‘smarter’,” Bossaerts said. “Because of the dopamine the drugs induce, we expected to see increased motivation, and they do motivate one to try harder. However, we discovered that this exertion caused more erratic thinking — in ways that we could make precise because the knapsack task had been widely studied in computer science.”