Last updated: May 19, 2016

When you think of attention deficit hyperactivity disorder (ADHD), you might picture a little kid who can't sit still in school. Turns out that for some people, ADHD symptoms may not appear until young adulthood, according to a new study published in JAMA Psychiatry

Researchers from King's College London looked at about 2,200 twins at ages 5, 7, 10, and 12 through mother and teacher reports. Then, when the twins reached age 18, the twins were interviewed and assessed for ADHD—defined by Diagnostic and Statistical Manual of Mental Disorders as “a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development in two or more settings." 

Of the subjects who were showing ADHD symptoms at age 18, 70% of them had not tested positive for ADHD during childhood. Although it's well established that childhood ADHD can continue into adulthood, this is among the first studies to examine late-onset ADHD

“This group showed significant levels of ADHD symptoms and impairment, as well as poor functioning and high rates of psychiatric comorbidity,” the authors write. “Therefore the absence of a childhood diagnosis of ADHD should not preclude adults with ADHD from receiving clinical attention.”