Hyperactivity, distraction, impulsivity — the hallmark symptoms of attention-deficit hyperactivity disorder (ADHD) have long been treated as a problem of the brain's executive function. A new review advances a bolder idea: circadian-rhythm disruptions are so common in people with ADHD that they may be part of the disorder itself, not merely a consequence of it.
The paper, published in Frontiers in Psychiatry, reviews dozens of related studies. The authors found that insomnia and other sleep problems affect up to 80 percent of adults with ADHD and up to 82 percent of children with the disorder — too prevalent to be a mere side effect. "The accumulated evidence demonstrates that circadian rhythm dysfunction is highly prevalent and clinically meaningful in a substantial proportion of individuals with ADHD," wrote Brandon Luu of Queen's University and Nicholas Fabiano of the University of Ottawa.
They stop short of one line: the paper does not argue that ADHD should be reclassified as a sleep disorder. But it does argue that internal-clock problems deserve serious attention from researchers and clinicians — not just a footnote in the chart.
The hypothesis rests on biological markers. The review cites evidence that melatonin production and cortisol cycles are often delayed in people with ADHD — the body's internal clock is shifted late. That matches a pattern clinicians have long seen: many ADHD patients can't fall asleep at night and can't get up in the morning.
A 2026 study in The Journal of Neuroscience made the picture more vivid with EEG: 32 medication-free adults with ADHD showed more frequent slow-wave brain activity — the signature of sleep — while awake and trying to sustain attention. Those slow-wave episodes lined up with attention lapses, slower reaction times, and more errors: parts of the brain briefly drifted toward sleep while the person was still on task.
If circadian disruption sits inside the causal chain, fixing the clock might ease the symptoms. The review cites a randomized trial that did exactly that: adults with ADHD and delayed sleep phase syndrome took low-dose melatonin, adopted earlier sleep schedules, and saw a 14 percent reduction in ADHD symptoms.
The authors also point to research suggesting that bright-light therapy — a standard treatment for circadian-rhythm disorders — can improve sleep patterns and reduce ADHD symptoms. Early evidence, but pointing the same way: treat the sleep, and the hyperactivity may follow.
The entanglement runs deeper than "bad sleep." A systematic review published in the Journal of Attention Disorders in September 2026, analyzing 11 longitudinal studies of 903 children, found that 44 percent of children with ADHD also had obstructive sleep apnea (OSA). And adenoidectomy — the common surgery for OSA — consistently improved both the apnea and the ADHD symptoms.
The review's message to clinicians is direct: pay closer attention to sleep and circadian-rhythm issues when evaluating patients with ADHD. After all, the poor concentration and memory problems caused by sleep apnea heavily overlap with ADHD symptoms themselves.
There's a longer tail to this research wave: days before the review, a JAMA Psychiatry study based on health records and genetic data from more than 187,000 adults age 50 and older linked ADHD to a significantly higher risk of mild cognitive impairment and dementia later in life. ADHD's footprint on health may be wider than previously understood.