A new study challenges previous research suggesting that there is an adult-onset version of attention deficit hyperactivity disorder (ADHD).

Adult-onset ADHD is said to develop after high school and is different from the adult version in which symptoms continue from childhood. Three large analyses have estimated that 3 to 10 percent of adults have adult-onset ADHD, The New York Times reported.

But a study published Friday in the American Journal of Psychiatry concluded that most cases of apparent adult-onset ADHD are actually substance abuse or mood disorders.

"This study carefully considered whether each person met criteria for ADHD and also fully considered other disorders" that might better explain the symptoms, said Mary Solanto, associate professor of pediatrics, School of Medicine, Hofstra/Northwell, The Times reported.

"In all those respects, it is the most thorough study we have looking at this issue," she added.

The study all but ruled out adult-onset ADHD as a stand alone diagnosis, according to Solanto.

However, other experts said it's too early to make a definitive conclusion and noted that attention deficits often begin before mood and substance abuse problems, which in turn can mask ADHD, The Times reported.