Adults

Three Misdiagnoses Before Anyone Said ADHD

August 11, 2026 · 5 min read

Last updated September 9, 2026

Adults who come in for ADHD testing have often been treated for something else first, sometimes for a decade. Anxiety. Depression. Burnout. A thyroid panel. Two rounds of an SSRI. Nobody in that chain was careless. The symptoms genuinely overlap, and the symptom the person reports — “I cannot concentrate” — belongs to all of them.

The scale of adult ADHD is easy to underestimate

The National Comorbidity Survey Replication estimated adult ADHD prevalence in the United States at roughly 4.4 percent, and found that the large majority of those adults were not being treated for it. Meanwhile the international consensus statement led by Stephen Faraone documents high rates of co-occurring conditions: mood, anxiety, and substance use disorders appear alongside ADHD far more often than chance.

That co-occurrence is exactly why the picture is confusing. If an adult has both ADHD and an anxiety disorder — a common combination — then treating the anxiety is not wrong. It is incomplete, and the residual attention problems get read as treatment resistance rather than as a separate condition.

The most useful discriminator in a careful evaluation is the timeline. Depression-driven concentration problems have a start date; the person can usually locate the year things changed. ADHD does not work that way. The DSM-5 criteria require several symptoms to have been present before age 12, and require impairment across more than one setting — not just at work, not just at home.

That childhood trail is often there even when nobody named it. It shows up in report cards, in the way a parent describes a bedroom, in a pattern of unfinished projects that predates every adult stressor the person can name. Retrospective self-report of childhood symptoms is imperfect, which is why collateral information from a parent, sibling, or long-term partner carries real diagnostic weight.

The second discriminator is what the inattention responds to

Anxiety-driven attention problems tend to track worry: they worsen with threat and ease when the stressor resolves. ADHD inattention is less tied to threat and more tied to the structure of the task — it appears reliably on boring, effortful, low-stimulation work, and can vanish on something urgent or interesting. Clinically that variability is often misread as proof the person could focus if they wanted to.

Sleep deserves its own mention

Chronic short sleep produces inattention, irritability, and executive dysfunction in anyone, and sleep problems are unusually common in ADHD — which makes the direction of causality genuinely hard to sort. Joel Nigg and colleagues have written about this bidirectional relationship. A responsible evaluation asks about sleep before it concludes anything.

This is why a fifteen-minute conversation and a symptom checklist is not enough. A checklist tells you what is happening now. Differential diagnosis is a question about history, setting, and course, and answering it takes a structured interview, standardized measures, information from someone who has known the person a long time, and a clinician willing to conclude that the answer is something other than ADHD.

Getting it right is not academic

Treat ADHD as anxiety and the person spends a year learning coping skills for a problem they do not have. Treat anxiety as ADHD and you may add a stimulant to an already activated nervous system. Both errors cost real time in someone’s life, and the second one can make things worse.