A new study finds that methylphenidate helps adults with ADHD weigh the costs of actions more accurately, improving decision-making that balances rewards against negative consequences. Conducted by Mads Lund Pedersen of the University of Oslo and colleagues, the study was published in Psychological Medicine. It used a double-blind, placebo-controlled crossover design involving 61 adults with ADHD and 63 healthy controls.
Attention deficit hyperactivity disorder is a neurodevelopmental condition marked by inattention, hyperactivity and impulsive behaviour, and people with the disorder often face choices that can lead to reckless outcomes. The experiment framed everyday decision-making as balancing the benefits of an action against its potential downsides, illustrating how choices unfold in real life.
Neurobiological theories suggest that the disorder involves atypical functioning of dopamine and norepinephrine, chemical messengers that regulate attention, reward processing and cognitive effort. Stimulant medications like methylphenidate increase the availability of these chemicals in the brain, and while researchers know stimulants generally improve decision-making, the precise psychological mechanisms have remained unclear.
The researchers recruited 61 adults diagnosed with ADHD and 63 healthy controls. Participants with ADHD completed testing twice, once after their standard dose of methylphenidate and once after a placebo, in a randomised, cross-over arrangement. The healthy controls also completed testing twice but did not receive medication.
During the experiment, participants engaged in a computer-based task designed to test how they integrate costs and benefits. In training, they learned to associate six different shapes with numerical rewards and six colours with numerical costs. In the main phase, a coloured shape appeared briefly and participants had to mentally combine the shape’s reward with the colour’s cost to determine a net value.
The researchers analysed the data using a framework known as the drift diffusion model, which separates the split-second process of choosing into distinct cognitive components. These include the drift rate, which measures how quickly information is accumulated; the decision threshold, representing how much information is required before acting; and non-decision time, which accounts for sensory and motor processes outside decision-making.
When unmedicated, participants with ADHD were less accurate than controls. The model showed they had a lower drift rate and a narrower decision threshold, meaning they processed information less efficiently and acted with less evidence.
Healthy controls tended to let the cost of the stimuli influence their decisions more than the benefits did, whereas unmedicated ADHD participants showed the opposite pattern, indicating a stronger sensitivity to benefit over cost.
Administration of methylphenidate changed information processing: it increased the drift rate, but the improvement was selective to the processing of costs, while sensitivity to benefits remained unchanged. This shift brought the behaviour of ADHD participants closer to that of the healthy control group in terms of cost sensitivity.
In addition, the medication produced some unexpected effects. Rather than increasing the decision threshold to encourage more cautious deliberation, the drug slightly narrowed the threshold further. It also increased non-decision time, which the researchers suggest might reflect a brief extra time spent encoding the stimuli and thereby improving representation and contributing to the higher drift rate observed under medication.
Across individuals, those reporting more severe daily symptoms had the lowest cost sensitivity when unmedicated. Among those taking methylphenidate, higher prescribed doses were associated with a stronger sensitivity to costs and a wider decision threshold.
The study notes several limitations to how the medication may act on the brain. It may enhance basic learning and memory rather than the moment of decision-making, as participants had to memorise shape–value associations during training. It is also possible that participants used mental arithmetic to subtract costs from benefits, a skill the stimulant could enhance independently of risk–reward weighing. The sample excluded individuals with severe comorbid psychiatric conditions, limiting generalisability, and the noticeable physical sensations some participants experienced could have given away when they received active drug, potentially influencing performance via expectancy effects.
Future research could separate these potential mechanisms by presenting the values directly on the screen, removing the need to memorise them during training.
The study, “Selective enhancement of cost sensitivity by methylphenidate in adult ADHD: a randomized placebo-controlled trial,” was authored by Mads Lund Pedersen, Athanasia M. Mowinckel, Sigurd Ziegler, Mats Fredriksen, Atle Bjørnerud, Tor Endestad, and Guido Biele.
