“My son was just diagnosed with ADHD, and I think I may have it, too,” says Alex, a 42-year-old salesman who presents for evaluation. In addition to being sad, anxious, and irritable, and meeting criteria for mild major depression, Alex says he is often bored at work, fidgety during meetings, and forgetful at home. He has had these problems since early college, and they fulfill the criteria for ADHD except that they are not traceable to his childhood.

Alex’s presentation will sound familiar to anyone who has treated ADHD. DSM-5 requires that ADHD symptoms begin before age 12, but there’s a new concept out there called “adult-onset ADHD.” So what do we make of his presentation? Is this really ADHD, or are the cognitive complaints a result of other causes such as stress, depression, and anxiety? To better understand this question, let’s start with some history.

History of the ADHD diagnosis
Early descriptions of ADHD date back to 1902, but the diagnosis really got its start in 1937 when Charles Bradley published the first report of amphetamine on behavioral problems and school performance. Over the years, the names of this syndrome have changed: minimal brain dysfunction (1960s–1970s), ADD (1980–1994), and ADHD (1994–present).

Throughout these changes, ADHD has always been depicted as a neurodevelopmental disorder, which means that—in the words of DSM-5—“ADHD begins in childhood.” Earlier DSM versions required that the symptoms begin before age 7, but DSM-5 relaxed the criteria to age 12.

Part of the reason for this change was that it’s difficult for older patients to recall their kindergarten years. There is also little difference between children who develop ADHD before age 7 and those who develop it between ages 8 and 12. They look similar in terms of family history, neuropsychological testing, psychiatric comorbidity, functional impairment, and course of illness (Faraone SV et al, Am J Psychiatry 2006;163(10):1720–1729; Willoughby MT et al, J Am Acad Child Adolesc Psychiatry 2000;39(12):1512–1519). That has caused some to speculate that ADHD symptoms beginning in the teen years, or even the adult years, may also represent the same syndrome.

Teen-onset ADHD
ADHD symptoms are difficult for patients to recall, so the best way to capture their true onset is to follow people prospectively over time. Three recent studies have done that. They followed a large cohort from early childhood to age 18 with regular assessment of ADHD and other symptoms, including parent and teacher reports. All of these found new-onset ADHD in the late teenage years after ruling out other causes of ADHD symptoms.

Is it possible that the studies missed the early presentation? Maybe. In one study, most of the teen-onset cases (75%) had sub-threshold ADHD symptoms before age 12, suggesting that they might represent a delayed onset of the full disorder (Cooper M et al, J Child Psychol Psychiatry 2018;59(10):1105–1113). The other two studies did not find childhood symptoms in the majority of the teen-onset cases (67%–87%), although one of them found high rates of childhood conduct disorder (29%) and oppositional defiant disorder (23%) in the teen-onset cases (Agnew-Blais JC et al, JAMA Psychiatry 2016;73(7):713–720; Caye A et al, JAMA Psychiatry 2016;73(7):705–712).

In summary, ADHD can start in the teenage years, but if you look hard enough, you’ll probably see some traces of the disorder in the patient’s childhood.

Adult-onset ADHD
In 2015, a study from Dunedin, New Zealand made headlines with the claim that the first evidence of adult-onset ADHD had been found. The study prospectively followed over 1,000 children from infancy to middle age. It compared ADHD at two time points: ages 5–7 and age 38. Childhood diagnoses were confirmed by parents and teachers, and adult diagnoses were made with structured interviews by raters who were blind to childhood diagnoses (Moffitt TE et al, Am J Psychiatry 2015;172(10):967–977).

The prevalence of ADHD in the Dunedin study corresponded to what we would expect: 6% in children and 3% in adults. But when the investigators looked at which individuals received the diagnosis, the results were stunning—there was virtually no overlap between children who were diagnosed with ADHD and adults who received the diagnosis.

Where did the new ADHD come from? It did not seem to develop gradually out of sub-threshold symptoms; 90% of the later-onset ADHD cases did not have ADHD symptoms as children. On the other hand, 30% of them had childhood histories of conduct disorder, so it may have been due to an ADHD-like pathology that was expressed differently in childhood.

Less clear is when this “adult-onset” ADHD began. The researchers did not ask the 38-year-olds that question, and did not interview them in their late childhood or teen years. While intriguing, these results fall short of proving “adult-onset” ADHD.

Potential causes
When ADHD begins after age 12, we are much less certain of what we’re dealing with, especially if it starts in adulthood. There are at least 3 possibilities to keep in mind:

1. Late-onset ADHD develops out of sub-syndromal childhood symptoms. This is suggested by some, but not all, of the studies.


2. Late-onset ADHD was present in childhood but the symptoms were forgotten. Recall of childhood symptoms is notoriously unreliable, which is why these studies used a prospective design to get around that problem. In practice, however, we don’t have that luxury, and many patients with valid adult ADHD simply don’t recall their childhood symptoms. Sometimes it’s suggested that the childhood symptoms were masked by a high IQ or supportive family, and while that makes intuitive sense, the prospective studies found the opposite pattern. Late-onset cases had slightly lower IQs and more psychosocial problems in their homes than healthy controls.


3. Late-onset ADHD is simply misdiagnosis of another psychiatric disorder. The 4 studies above ruled out other psychiatric causes of the ADHD symptoms (except personality disorders), but a smaller study found strong support for the misdiagnosis theory. They followed 239 children from ages 10 to 25 with regular assessments from parent, teacher, and self-reports along the way. None of the children had ADHD at the start of the study, and 17% developed ADHD after age 12. However, 95% of these late-onset cases could be attributed to substance use or other mental disorders (Sibley MH et al, Am J Psychiatry 2018;175(2):140–149). (See “Adult ADHD: What Else Could It Be?” above for more on those possibilities.)

Back to Alex. His symptoms began in his late teens, so based on these new studies, it’s possible he has ADHD. His family history also points that way. After ruling out other causes of adult ADHD, we might consider starting an antidepressant with benefits in ADHD, like bupropion, or a stimulant. Alex has mild depression, but those symptoms might clear up as his functioning improves with stimulant treatment.

If using a stimulant, we’d need to watch Alex carefully because we don’t have confirmation that his ADHD began before age 12. If he tries taking a stimulant and the benefits keep wearing off, we should reconsider the diagnosis instead of raising the dose beyond the maximum in the PDR.

TCPR Verdict: Teenage-onset ADHD does exist, although many of these patients had behavioral problems or milder symptoms of ADHD in their childhood years. Adult-onset ADHD, however, has not been confirmed. When patients present with ADHD symptoms that began after age 12, look carefully for other causes, and monitor closely if stimulants are used.