Discovery of Adult-Onset ADHD Raises Questions

Four recent studies have turned what we know about attention-deficit/hyperactivity disorder (ADHD) on its head. By following large cohorts from early childhood to adulthood, they’ve claimed to discover that ADHD can start in adults who did not have the disorder before the DSM-5 cutoff of aged 12 years. But before we rewrite the DSM and start prescribing stimulants to every adult who cannot concentrate, let’s look at what is missing in this research.

In 3 of the 4 papers, the “adult-onset” ADHD began in the teenage years.^1-3 Furthermore, many of these teen-onset cases (29% to 75%) had symptoms of ADHD in their childhood that were either below the threshold for the full diagnosis or were classified as part of a related disorder (eg, conduct disorder or oppositional-defiant disorder).

The fourth paper claimed to identify new onset ADHD in middle aged adults, and it is one that made the biggest headlines.⁴ The study followed a group of over 1000 residents of New Zealand from aged 3 to 38 years as part of a larger investigation on the effects of adverse birth experiences on health. They gathered symptoms of ADHD at 3 time points: Ages 5 to 7; 11 to 15; and finally at age 38. What they discovered surprised them. Most of the children with ADHD no longer had the full disorder as adults, and most of the adults who met criteria for ADHD in middle age did not have the full disorder in childhood. The problem with this surprise discovery is that they did not ask the participants when their ADHD symptoms began, so these may have been teen-onset cases like we saw in the other 3 studies.

When someone goes through the effort to see a psychiatrist, there is a good chance that they have a real psychiatric problem. Or, as Groucho Marx put it, “Anyone who goes to a psychiatrist ought to have their head examined.” With community samples, the working assumption is that the patients are normal (and don’t need their heads examined), which is why this kind of research is so prone to false positives. The false positives in these community studies were further elevated by their reliance on self-report.⁷

Although these studies attempted to rule out other causes of adult-onset ADHD, those exclusions are hampered by false-negative rates. For example, it is not unusual for patients to forget past episodes of mania or psychosis, and those episodes often cause long-standing cognitive problems that could be mistaken for ADHD. Some important causes, like autism spectrum or personality disorders, were not evaluated in these studies.

But what if—even after siphoning those off—there remains a small number of people whose ADHD genuinely begins in adulthood? These studies point to that possibility, but they don’t tell us whether these cases share common biological markers, familial patterns, and treatment response with childhood-onset ADHD. The gender distribution, for example, was different, with more males in the childhood-onset cases.

In practice, the first thing to do when a patient presents with adult-onset ADHD is to screen for other psychiatric disorders that might explain it. Medical and environmental factors can also cause ADHD-like symptoms, including age-related cognitive decline, sleep deprivation, sleep apnea, inflammation, obesity, air pollution, chemical exposure, and excessive use of digital media.^8-12 Patients who suffer from these problems might ask their doctor for a stimulant, but none of those syndromes demand a psychopharmacologic approach.