HQ Team
July 2, 2025: A majority of clinical research on adult Attention Deficit Hyperactivity Disorder (ADHD) suffers from serious methodological shortcomings, making it difficult to use the results in practice, according to researchers from the University of Copenhagen and the University of São Paulo.
Initially developed for children, the diagnosis of ADHD is often difficult to make in adults, partly because the diagnostic criteria are based on behaviour in children.
When diagnosing adults, however, these criteria are often based on adults’ subjective experiences, such as having difficulty concentrating or being very impulsive.
“The rising number of adults diagnosed with ADHD raises important questions about diagnostic validity, especially since many were never identified in childhood and are now seeking help, sometimes prompted by ADHD content on social media,” Associate Professor and senior researcher, Dr Igor Studart, at the University of São Paulo said.
“That made us curious: how have randomised controlled trials on ADHD dealt with this diagnostic challenge?”
Similar symptoms
The disorder shares its symptoms with several other mental disorders, such as depression, schizophrenia, and bipolar disorder, making it crucial to exclude these disorders when diagnosing ADHD. This requires a thorough diagnostic assessment by an experienced psychologist or psychiatrist.
It is not always the case that such a thorough assessment is made, and researchers said even psychiatric research into ADHD often neglects this fundamental work.
“We have examined how 292 of the most credible studies in evidence-based medicine – the so-called randomised controlled trials – diagnosed their adult subjects,” said University of Copenhagen Professor of Psychiatry and Consultant Psychiatrist Julie Nordgaard.
“We conclude that half of the studies did not ensure a broad and thorough diagnostic assessment of the patients before the trial to rule out other disorders. This means that they can’t know if their subjects have other mental disorders, such as depression or schizophrenia.
“And that’s not all. More than half of the studies included subjects who have also been diagnosed with other mental disorders, making the diagnosis even more difficult to allocate,” she said.
‘Problematic’
These methodological shortcomings are problematic because they imply that it is impossible to know which disorders and symptoms the treatment investigated in these trials were potentially affected.
ADHD is a mental disorder that develops in children suffering from attention deficit disorder, hyperactivity and impulsivity. More adults today are being diagnosed with ADHD. Worldwide, it is estimated that more than 300 million adults have the disorder, and in Denmark, too, the diagnosis is growing rapidly.
In children, the diagnosis is made based on observations of the child’s behaviour by parents and teachers. In adults, the same diagnostic criteria are often based on subjective experiences or the adult’s own experiences.
Randomised controlled trials are trials where subjects are randomly assigned to one or more groups to study the effect of a certain treatment. One of the groups, the control group, receives either no treatment, a placebo or a standard treatment, while the subjects in the other groups receive the treatment under investigation.
It is this type of trial that is considered the gold standard in evidence-based research.
Not trained professionals
According to the researchers, one of the problems with the diagnostic assessment in many of the clinical trials is that it seems to have been carried out by people who are not trained to do so. And often with methods that are not thorough enough.
“In 61% of the studies, they do not state who diagnosed the subjects,” said Mads Gram Henriksen, Associate Professor and Senior Researcher at the University of Copenhagen. “In only 35% of the studies, it is stated that a psychiatrist or psychologist made the diagnosis.
“But diagnostic assessment should always be performed by an experienced professional with the necessary training to ensure that the diagnosis is made correctly, and this should be stated in the study’s method section.”
In some cases, the assessment and the diagnosis were made by the subject themselves, and in one particularly egregious case, it was done with the help of a computer, the researchers said.
“In psychiatry, we need that all diagnoses, not just ADHD, are made with the same uniform criteria and by trained professionals. Otherwise, we cannot rely on the results or compare them across studies,” said Julie Nordgaard.
“Especially in a situation where a diagnosis such as ADHD in adults is increasing, we need to be very thorough and have a solid foundation. Otherwise, we risk too many people getting a wrong diagnosis and not being able to give them the most effective treatment. Or they risk receiving unnecessary treatment that causes side effects.”
The study Diagnosing ADHD in adults in randomised controlled studies: A scoping review was published in the journal European Psychiatry.
