Are You Interested in ADHD Research? Here’s Where to Start
A reader recently asked me, in reply to a recent blog post about Russell Barkley, what important research is being done on ADHD, and who is doing it.
The best place to start exploring ADHD research is with the World Federation of ADHD International Consensus Statement (open access PDF here). This 2021 meta-analysis lists 208 evidence-based conclusions about ADHD.
It makes an excellent introduction to ADHD research because it spans a variety of topics, including:
Who has ADHD and how common it is worldwide
Genetic and environmental causes,
How the brain differs in ADHD,
How ADHD affects skills in cognitive and academic areas,
What treatments are safe and effective,
What life outcomes affect people with ADHD -- including educational achievement, peer relationships, health problems, rates of accidents and substance abuse, quality of life, and more.
The paper is well organized, with the conclusions placed under clear, useful topic headings.
The writing style seems clear, and fairly easy to read. There’s not much jargon, as research papers go. However, I’m a former cognitive neuroscientist who has probably read thousands of research papers, so your mileage may vary, depending on your experience reading psychology and neuroscience research papers.
Who:
There were 80 authors from 27 countries and 6 continents, led by prolific researcher Stephen V. Faraone.
Authors were representatives of national and international ADHD organizations, such as the World Federation of ADHD, EUropean NETwork for Hyperkinetic DisorderS (Eunethydis), the Latin American League of ADHD, the Chinese Society of Child and Adolescent Psychiatry, etc.
What they Did:
1. The authors reviewed studies that had at least 2,000 participants, meta-analyses of five or more studies, and meta-analyses with at least 2,000 participants.
2. Based on this research, the authors created 208 evidence-based statements about ADHD.
3. Finally, 403 people read the manuscript and agreed with its contents.
Why:
This was the second international consensus statement written about ADHD. It updates the original statement by “cataloging important scientific discoveries from the last 20 years.”
“Nearly 2 decades ago, an international team of scientists published the first International Consensus Statement on ADHD. They sought to present the wealth of scientific data attesting to the validity of ADHD as a mental disorder and to correct misconceptions about the disorder that stigmatized affected
people, reduced the credibility of health care providers, and prevented or delayed treatment of individuals challenged by the disorder.” [bold added by me].
Keep in mind that not every interesting topic in ADHD research is covered:
“If a topic is not included in this document, it does not mean the topic is unimportant; rather, it means the evidence found was insufficient to allow firm conclusions. This could be because there were insufficient studies of quality, because no attempt was made to assess publication bias, or because the data available did not support the claims made.”
What they Found:
Here are some of the conclusions I think will be most interesting and important to ADHD people and their supporters:
ADHD is not new. Signs and symptoms have been recognized as clinically significant for over 200 years.
The diagnosis of ADHD is valid, based on standard criteria for the validity of a mental disorder.
ADHD occurs throughout the world. It affects about 6% of youth and 3% of adults, and is more common in males than females.
ADHD has not become more common in the past 30 years.
There are many genetic and environmental causes for ADHD.
Environmental causes typically affect fetuses and newborns. Environmental causes include: exposure to toxins; nutrient deficiencies; very/extremely preterm birth or low birthweight; extreme deprivation, stress, infection, poverty, or trauma early in life; or traumatic brain injury early in life.
There are differences in the brain between groups of people with and without ADHD. However, these are not useful for diagnosing ADHD. First, these differences are typically small. Second, they do not differ between ADHD and other disabilities.
Differences in the brain are structural (such as cortical surface area, gray matter volume, white matter integrity) and functional (activation in specific areas in general and while doing specific tasks, as measured by fMRI and electroencephalogram activity).
ADHD medications do not change brain structure. They do affect brain function, especially in inferior frontal and striatal areas that are atypical in ADHD.
As a group, people with ADHD have deficits in a variety of abilities measured with psychological/neuropsychological tests, including: academic achievement (reading, spelling, arithmetic); working memory; various forms of attention; planning and organization; impulsive decision making; and a preference for small immediate rewards over large delayed rewards.
Some medical problems are more common in ADHD, including allergies and asthma; obesity; sleep disorders; somatic disorders; and more.
ADHD can reduce quality of life for young people and their parents, relative to typically developing young people and their parents.
Children and youth with ADHD are more emotionally disregulated. They may be more emotionally reactive to novel or stressful events.
Children and youth with ADHD are more likely to have emotional problems, conduct problems, or peer problems/difficulty socializing with and rejection by peers, and to engage in bullying.
Children and youth with ADHD have higher rates of accidental injuries and traumatic brain injury (TBI), substance use disorders, risky behavior, and premature death.
Children and youth with ADHD have higher rates of suicide.
People with ADHD are more likely to be both perpetrators and victims of crime. However, they are also more likely to make false confessions.
People with ADHD are more likely to experience educational underachievement, such as lower achievement, needing special education services, dropping out of school, or not graduating high school on time.
Several medications are safe and effective for treating ADHD symptoms, including both stimulant and non-stimulant medications. These medications have specific adverse effects, including on sleep and children’s height gain.
Some non-medication treatments for ADHD are safe and effective, including “behavioral and cognitive-behavioral therapies,” computer-based cognitive training and neurofeedback, omega-3 fatty acid supplements, and exercise.
What’s Next?
Remember that not every research finding about ADHD was included in the paper. The Discussion section lists things we still need to learn more about. Here are some of my favorites:
How culture affects the way ADHD manifests and responds to treatment
How ADHD affects older adults
Effects of stigma on people with ADHD
The nature of emotional regulation symptoms of ADHD, and whether they should be added to the diagnostic criteria
In addition, I noticed some topics were missing despite a large body of research exploring them, and in my opinion, good evidence (at least from studies with fewer than 2,000 participants):
The overlap between ADHD and other developmental disabilities, such as autism, dyslexia, dyscalculia, and developmental coordination disorder (DCD)/dyspraxia.
The role of dopamine in ADHD.
The rates of anxiety and depression in people with ADHD.
Variability in performance (especially response time) from moment to moment, which researchers call “intra-individual variability,” and which I’ve read is perhaps the best-supported symptom of ADHD -- is mentioned as part of the findings of one meta-analysis (#67), but not as a fact about ADHD in its own right.
How can I use the paper to learn more?
Here are some ways you can use this paper as a jumping-off-point to learn more about research findings that interest you. These suggestions are aimed mostly at people who don’t read a lot of research papers, so feel free to ignore them if you have more experience.
1. First, see Table 1 for the summary of findings. You can follow links from the table to whichever findings most interest you.
2. Read the introduction, discussion, and the sections that interest you.
3. Look at the references for claims that seem interesting or surprising.
Who wrote these papers? Check out the authors’ websites, and see what they’re studying. Search Google scholar for their names, and you will find a list of their papers, which you can sort by date.
4. Follow up by reading interesting cited papers: The easiest way to find specific papers is to search Google scholar for the titles. You can always find the abstracts free at the publisher’s website. On Google Scholar, you can often find a free pdf of the full text on the right-hand margin of the page. (If you don’t see one there, click the button “See x versions” next to the link to “Related articles”).
Have you read the International Consensus Statement? What did you think? Did anything in it, or not included, surprise you?
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