The question of whether ADHD is real is a non-question. Over and over, studies turn up differences between the brains and the life outcomes of people with and without ADHD.

So let’s instead look at a somewhat similar question that does have some scientific merit: is adult-onset ADHD real?

If you ask the DSM, the manual that psychiatrists in the United States commonly use to diagnose ADHD, the answer is no. According to the DSM, a diagnosis of ADHD by definition requires that symptoms show up by 12 years of age – there’s no adult ADHD without childhood ADHD.

DiagnosisSo, case closed? Not quite.

The DSM’s guidelines for diagnosis are created by committee. What that means is that while the broad outlines of what ADHD is are well established by the science, the more technical details about how exactly ADHD is defined have a touch of arbitrariness in them.

For example, the last version of the DSM required that people show symptoms of ADHD by age 7 to qualify for diagnosis. So someone whose symptoms emerged at, say, 9 years old, would qualify for a diagnosis of ADHD under the current version of the DSM but not the previous version.

Part of the reason for these changes is to reflect our evolving understanding of ADHD. And this gets at the heart of things: there’s a lot we do know about ADHD (some of the main impairments associated with it, its implications for life outcomes, the fact that it’s highly heritable, etc.), but there’s a lot we don’t know about how ADHD develops.

Which leads us back to the question of when does ADHD have to show up to be ADHD? The truth is that we don’t really know, because we don’t understand exactly what causes ADHD to develop in the first place.

We do have reason to believe that adult ADHD is rare, if it exists at all. For example, a recent study showed that in a group of 446 adults with ADHD, only 6.9 percent reported experiencing the onset of symptoms in adulthood. And only 2.8 percent had adult-onset ADHD without having any other disorder.

The authors of that study point out that when people appear to have adult-onset ADHD, it’s important to look carefully for other conditions that “mimic” ADHD given how rare adult-onset ADHD is.

Another possibility worth considering is that people who seemingly develop ADHD symptoms as adults may have had ADHD symptoms all their lives but only recently been put into an environment that makes their symptoms obvious.

This is true not just for “adult-onset” ADHD, but for anyone whose symptoms appear after the DSM’s cutoff age of 12.

For example, if someone’s symptoms show up at the age of 14, do they simply not qualify for a diagnosis? It’s important to look at the possibility that they actually did experience ADHD symptoms earlier but that the symptoms were less impairing because they had lots of support, their environment didn’t make as many demands on them, they were able to compensate in other ways, etc.

So the bottom line is that we don’t know much about adult-onset ADHD, including whether such a thing even exists. But we do know that given how rare it seems to be for ADHD symptoms to emerge only in adulthood, it’s worth looking at alternative explanations like other disorders or the possibility that the symptoms were lurking there all along when people appear to develop symptoms as adults.

Also, if any ADHD Millennial readers have experienced adult-onset ADHD (or “adult-onset ADHD” that turned out to be something else), I’d be really interested to hear about your experiences!

Image: Flickr/Ilmicrofono Oggiono