What Else Could Adult ADHD Be?

October 1, 2026by Chris Aiken, MD0

The ASRS rating scale above didn’t clarify whether cognitive symptoms were due to ADHD or other disorders in adults. Nor does computerized testing.

Half of US adults with ADHD received their first diagnosis after age 18

STUDY: Cuomo A et al, Brain Sciences 2026

STUDY TYPE: Narrative review

FUNDING: Independent

Background

In 2023, about 1 in 17 US adults reported a current ADHD diagnosis, and half were first diagnosed as adults. Some of that rise reflects missed cases, especially in women and people with inattentive symptoms. This narrative review asked how often a first-time adult diagnosis reflects another condition, and how to tell the difference.

Results

ADHD changes with age. Childhood hyperactivity gives way to inner restlessness, disorganization, procrastination, and impulsive decisions in adults. Many adults cycle between full and partial symptoms.

Four changes help explain the rise in adult diagnoses:

DSM-5 raised the age of onset from 7 to 12 and lowered the adult symptom threshold from six to five. In one sample, prevalence rose from 2.8% to 3.55%.
Better recognition of women and inattentive presentations.
Wider access, including telehealth, which about half of adults with ADHD used for care.
Misdiagnosis of adult-onset ADHD without childhood precedents.

Late-onset cases rarely held up. In the MTA cohort, repeated assessments with multiple informants confirmed only about 1 in 20 apparent late-onset cases. In the rest of the cases, the ADHD was traceable to unreported childhood ADHD symptoms (ie, real ADHD) or adult problems that impair cognition like substance use, another psychiatric disorder, and medical or sleep disorders. Sometimes the symptoms were temporary, and likely due to task overload.

The ADHD screening scale (ASRS) did a poor job separating ADHD from inattention due to anxietydisorders. Adults also recalled childhood symptoms poorly, usually underreporting them.

Notably, a good response to a stimulant did not confirm the diagnosis.