ADHD News & Research

Study: Adult ADHD and Childhood ADHD May Be Separate Disorders

Controversial new research suggests that people who showed no signs of ADHD as children may develop the condition later in life and, conversely, children with diagnoses may outgrown their symptoms.

July 19, 2016

Two new studies suggest that adult ADHD is not simply a continuation of childhood ADHD, but actually a separate disorder with a separate developmental timeline. And, what’s more, adult-onset ADHD might actually be more common than childhood-onset. Both of these findings fly in the face of popular belief, and beg to be verified with more research.

The two studies, published in the July 2016 issue of JAMA Psychiatry, used similar methodology and showed fairly similar results. The first, conducted by a team at the Federal University of Rio Grande do Sul in Brazil, evaluated more than 5,000 individuals born in the city of Pelotas in 1993. Approximately 9 percent of them were diagnosed with childhood ADHD — a fairly average rate. Twelve percent of the subjects met criteria for ADHD in adulthood — significantly higher than the researchers expected — but there was very little overlap between the groups. In fact, only 12.6 percent of the adults with ADHD had shown diagnosable signs of the disorder in childhood.

The second study, which looked at 2,040 twins born in England and Wales from 1994-5, found that of 166 subjects who met the criteria for adult ADHD, more than half (67.5 percent) showed no symptoms of ADHD in childhood. Of the 247 individuals who had met the criteria for ADHD in childhood, less than 22 percent retained that diagnosis into adulthood.

The findings of the two reports confirm findings from a New Zealand study, published in October 2015, that followed subjects from birth to age 38. Of the patients who showed signs of ADHD in adulthood in that study, a whopping 90 percent had demonstrated no signs of the disorder in childhood.

The combined results of these studies suggest that the most widely accepted definition of ADHD (as a disorder that develops in childhood and is occasionally “outgrown” as the patient ages) may need reassessment. Some experts remain doubtful, however, and suggest that the study’s authors may have simply missed symptoms of ADHD in childhood in cases where it didn’t seem to become apparent until adulthood.

“Because these concerns suggest that the UK, Brazil, and New Zealand studies may have underestimated the persistence of ADHD and overestimated the prevalence of adult-onset ADHD, it would be a mistake for practitioners to assume that most adults referred to them with ADHD symptoms will not have a history of ADHD in youth,” write Stephen Faraone, Ph.D., and Joseph Biederman, M.D., in an editorial cautioning the ADHD community to interpret the two most recent studies with a grain of salt. They called the findings “premature.”

In both studies, however, those with adult ADHD showed high levels of criminal behavior, substance abuse, traffic accidents, and suicide attempts. These disturbing correlations remained even after the authors adjusted for the existence of other psychiatric disorders — proving once again that whether it develops in childhood or adulthood, untreated ADHD is serious business.