Can ADHD Really Start in Adulthood?
Some researchers say there's a new type of ADHD that develops on a different timetable. Understanding disabilities gives us better explanations.
The Problem
What if we recently discovered a new disability that looks just like ADHD except that it starts in adulthood?
And what if there are more adults with this new disability than with ADHD as we currently know it?
These controversial claims come teams doing credible research. Three groups (in New Zealand, Brazil, and the UK) ran longitudinal studies with hundreds to thousands of people: the best way to study how people gain or lose a disability over their lifetime. One team was even conducting a twin study, the method used to study the influence of genes while keeping environments as consistent as possible.
These researchers assessed all participants for possible ADHD, using DSM-5, as children and as adults. Many people had the symptoms necessary for an ADHD diagnosis as adults, but not as children — a pattern we can call “adult onset ADHD.”
“Adult onset” people have the same symptoms as people with typical ADHD, and the same life problems. They have the same tendency toward reduced educational achievement and employment, poor driving, criminal behavior — and, in all studies, mental illness and substance abuse. Yet, by definition, they can’t have ADHD.
To qualify for an ADHD diagnosis (in DSM-5), a person must have “several inattentive or hyperactive/impulsive symptoms before” age 12. The DSM-5 assumes that ADHD is a “neurodevelopmental disability,” a lifelong, heritable condition that affects how a person develops. It further assumes that a condition present by birth will cause visible problems in multiple environments before puberty.
How do we make sense of people who have all the characteristics of ADHD except for age of onset? If they don’t have ADHD, what do they have?
These 3 research groups make the radical claim that people with “adult onset ADHD” are more than just people who happen to be diagnosed as adults.
Instead, these researchers argue, “adult onset” people couldn’t be diagnosed as children because they didn’t have ADHD brains then. They developed ADHD-like brains in adulthood, in the same way that people with schizophrenia start developing symptoms as teenagers and adults.
Thus, they claim, “adult onset ADHD“ is “not a ‘neurodevelopmental disorder.”
Because ADHD as we know it and “adult onset ADHD” involve different neurotypes—heritable patterns of brain development—they must be “distinct syndromes.”
The Controversy
The idea that “adult onset” ADHD is a new condition has sparked controversy, for several reasons.
First, it’s not a parsimonious explanation.
It’s like claiming a new fossil belongs to a new species instead of being, say, a younger specimen of an existing one (which has often happened in paleontology). It makes for an unnecessarily “messy” universe.
When we have likely alternative explanations, there’s no good reason to assume a whole extra entity exists.
More importantly, we haven’t ruled out one obvious alternative explanation: “Adult onset” ADHD people are just people with ADHD who could have been diagnosed as children, but weren’t.
Although they met ADHD criteria, their symptoms were unseen or unexplored at the time. Later, they were missed by the researchers trying to diagnose them retrospectively. After all, in some ways, retrospective diagnosis is even more difficult than normal diagnosis: one must contend with the way memory distorts over time.
One crucial piece of evidence that “adult onset” people were simply missed is that the populations overrepresented among “adult onset” people are the same ones often overlooked or misdiagnosed among ADHD children: girls and people with high IQ.
Only one study even addresses, and tries to rule out, the possibility of missed childhood diagnoses!
According to a review of the quality of studies on “adult onset” ADHD, current evidence isn’t strong enough to distinguish between 3 possible explanations:
1) “adult onset” ADHD truly begins in adulthood;
2) “adult onset” ADHD is just undiagnosed childhood ADHD; or
3) methodological problems create the illusion of “adult-onset ADHD.”
I believe methodological problems account for some cases of “adult onset” ADHD. However, the sheer number of cases suggests there must be additional causes.
Most of the urgency of the debate comes from concern about the practical consequences of recognizing “adult onset ADHD” as a new entity. How would it affect diagnosis and treatment of ADHD, and the new condition itself? There will be a huge impact, because the “adult onset” population is immense. If classed as having ADHD, they would make up between half and 90% of adults with ADHD.
Of course, when a new diagnosis is introduced to the medical care and health insurance systems, bureaucratic issues will inevitably slow care. Furthermore, the same resources for treating adult ADHD could be divided among many more people.
Fortunately, we can explain “adult onset” ADHD without proposing a new condition.
“Adult onset” ADHD is real, in the sense that some people really do meet criteria for ADHD diagnosis as adults but not as children. However, they have the same underlying condition as people with typical ADHD. They just fit better into their childhood environments.
“Adult onset” people are those who manage the longest before their environments overwhelm their capabilities.
Some researchers, including big names like F. Xavier Castellanos and Stephen Faraone, support this explanation.
When you understand that a disability is an interaction between a person’s body and their environment, an environmental explanation seems most plausible.
The Gene-Environment Interaction
Researchers who see “adult onset ADHD” as a separate condition assume that because these people didn’t have a disability as children, they also lacked the impairments that come with ADHD (difficulty controlling attention, impulsive behavior, disorganization, etc.).
That doesn't follow.
As I explain elsewhere, the same person, with the same brain and capabilities, can have a disability in one environment but not another. In fact, ADHD “experts” have long explained this phenomenon using ADHD as an example.
Most likely, people with “adult onset ADHD” have the same neurotype as ADHD people, with the same basic difficulties. There’s even evidence the same genes underlie both “conditions.”
However, people with “adult onset ADHD” grow up in more supportive or less demanding environments.
As people age, the world requires ever higher levels of executive functioning. Eventually, people with ADHD neurotypes can no longer keep up with the world’s demands. Then, they show the symptoms listed in the DSM-5: they have a disability.
The age at which the disability emerges depends on several factors. These include:
the magnitude of a person’s ADHD impairments;
the person’s ability to compensate;
the supportiveness and structure of the person’s environments; and
the level of executive functioning expected.
As you might expect, people can function, and hide their disability, better when they:
have parents who provide both support and structure (studies 1,2,3).
have fewer, or less intense, ADHD symptoms.
are valued for their strengths, not just criticized for their difficulties.
have special talents or high IQ, areas that help them compensate and even succeed. (UK, New Zealand, and Brazilian studies, and others).
are quiet, well behaved, even seen as good students.
work hard and invent coping strategies (such as teaching themselves mnemonic devices, or packing their lunch the night before so they remember to bring it to school).
attend schools flexible enough to communicate with families and modify assignments in ways that reduce the executive function burden.
Think of the disability of ADHD as a continuum. Some children, with severe impairments, demanding environments, and limited support, can be diagnosed as early as preschool. Other people don’t fall behind until college, graduate school, and beyond. The environments in which people live, and the way they deal with difficulties, determine when the disability emerges.
In short: people with “adult onset” ADHD are those who last the longest before life’s executive functioning demands overwhelm them.
People with “Adult Onset” ADHD are neurodivergent
People with “adult onset ADHD” aren’t typically developing kids whose development suddenly veers off towards ADHD. They were always neurodivergent.
They had higher rates of:
tics,
oppositional behavior and oppositional defiant disorder (see UK study),
conduct disorder (see New Zealand, UK, and Brazilian studies), and
All these disabilities often come with ADHD.
In a study of adults born in the 1990s and diagnosed with ADHD in their communities, 42% received a psychiatric diagnosis other than ADHD — as compared to 1% of a neurotypical comparison group).
People with “adult onset ADHD” also had childhood ADHD symptoms; just not in the necessary number and intensity to be diagnosed. In one study, “adult onset” people had three times more childhood ADHD symptoms than did a neurotypical comparison group. Both parents and teachers reported elevated symptoms of ADHD.
In a highly educated sample of clinic-referred adults, where 50% qualified for a childhood diagnosis, an additional 25% did not, yet had 4 childhood symptoms (an unusually high number).
In fact, a large majority of “adult onset” people may have childhood ADHD symptoms or behavior problems. For example, in the Brazilian study, only 38% of participants with “adult-onset ADHD” lacked symptoms of ADHD and conduct disorder.
Faraone and Biederman call this limbo of high ADHD traits, yet not enough for diagnosis, “subthreshold ADHD.” People with “adult onset ADHD” usually have “subthreshold ADHD” as children. Those who showed sub-threshold signs of ADHD as children were more likely to be diagnosed with ADHD as adolescents. If that pattern continues, they’ll also be more often diagnosed as adults.
In short, evidence supports the idea that people with “adult onset ADHD” have the same pattern of brain development, inattention, hyperactivity, and impulsivity as those with diagnosable ADHD — only their environments differ.
The DSM Needs to Change
I agree with the DSM-5 that ADHD traits exist before age 12. From birth, a person has certain patterns of brain development that predisposes them to inattention, hyperactivity, and/or impulsivity. However, the DSM also assumes that these executive functioning difficulties will necessarily be obvious and cause problems in multiple environments before age 12. I disagree.
I believe the age of onset criterion is arbitrary. Studies already support the idea that ADHD can “originate” in adolescence. I think that we should remove the age limit. If ADHD is, in fact, a continuum, then an age limit makes no sense.
The Future of “Adult-Onset” ADHD
However we explain it, there are many people who first show clear signs of ADHD in adulthood. That means there are many more adults with ADHD than we currently believe. Thus, it becomes even more urgent to make our schools, workplaces, and public spaces accessible to people with ADHD…and people with “sub-threshold” ADHD.
We also need more — and more rigorous — research on what people with ADHD traits need to succeed. What are people with “adult onset” ADHD, their families, schools, and communities, doing right? How can we replicate such circumstances for people diagnosed younger?
What do you think? Do you think “adult onset ADHD” is a new condition, just ADHD people who were missed in childhood, or an illusion caused by flawed study methods? Do you know anyone with “adult onset ADHD”, or are you such a person yourself?
Should there be an “age of onset” limit for ADHD, or any developmental disability?
How will the world change if we recognize “adult onset ADHD?”
Hit the button below to share your thoughts:
Read More
Here’s what to read if you’d like to learn more about the evidence on “adult onset ADHD.”
Start with these Overviews
Is adult-onset ADHD a distinct entity? by F. Xavier Castellanos (2015) is a readable introduction to the terms of the debate and what’s at stake.
Can attention deficit/hyperactivity disorder onset occur in adulthood? by Stephen V. Faraone and Joseph Biederman (2016) is a fantastic overview from a skeptical perspective.
Studies Claiming Adult Onset ADHD is a Distinct Condition
Note: research papers often call this condition “late onset ADHD,” which is less clear than the term I use here, “adult onset ADHD.”
This study by Terrie E. Moffitt and colleagues (2015) in New Zealand — catchily titled “Is adult ADHD a childhood-onset neurodevelopmental disorder? Evidence from a four-decade longitudinal cohort study”— started it all.
“Attention-deficit/hyperactivity disorder trajectories from childhood to young adulthood: evidence from a birth cohort supporting a late-onset syndrome” by A. Caye and colleagues (2016), a Brazilian team.
Persistence, Remission and Emergence of ADHD in Young Adulthood: Results from a Longitudinal, Prospective Population-Based Cohort, by Jessica Agnew-Blais, Terrie Moffitt, and colleagues (2016) in the UK.
Alternative Explanations and Evidence
[Review] Adult-Onset ADHD: A Critical Analysis and Alternative Explanations. Taylor and colleagues (2022) evaluated the quality of “adult onset ADHD” studies using widely accepted criteria. They found that the empirical evidence wasn’t strong enough to support any particular explanation.
[Experiment] The Prevalence of “Late-Onset” ADHD in a Clinically Referred Adult Sample by Mary V. Solanto (2019). A large clinical sample of adults diagnosed with ADHD was retrospectively assessed for childhood ADHD. Half the sample met full criteria, while an additional 25% met less stringent criteria.
[Experiment] Late-onset” ADHD symptoms in young adulthood: Is this ADHD?. In this prospective study, Lucy Riglin and colleagues (2022) find that “childhood resources may delay the onset of ADHD” into adolescence or adulthood.
[Review] Symptoms in individuals with adult-onset ADHD are masked during childhood.” Hirotaka Kosaka and colleagues (2019) note that people with adult-onset ADHD have higher IQ, thus more “resources” to use for functioning. Using an iceberg metaphor, they explain how differences in IQ and environments affect the age when a person becomes disabled. A person has more resources than just IQ, but this gets across the basic idea.
Major eye rolling over here about the idea of “adult onset ADHD” being a separate experience from childhood ADHDers. IMO it’s just another in the long list of neuronormative research observing behavior and trying to make sense of it without sufficiently asking the people actually having the experience.
For me, along with many other late identified ADHDers, it was the load of raising children, working, and keeping a house running that brought up the possibility of ADHD - which you allude to with demands surpassing capacity at a late age.
Another interesting piece to bring in is the ongoing heaviness of late stage capitalism on everyone. That may lead to an increasing number of people considering ADHD as a possibility for themselves, as we have so little access to safety nets or community more broadly. As the window of neuronormativity becomes smaller, more and more people identify as neurodivergent.