Brain Studies Show ADHD Is Real Disease

One expert said the study may be a milestone in understanding ADHD.

"This is a very important study as it adds increasing evidence that ADHD is a heritable disease with genetically determined neurobiological underpinnings and adds further evidence that this is a valid mental disorder, often requiring neurobiological interventions [such as] psychopharmacological treatment," said Dr. Jon A. Shaw, professor and director of child and adolescent psychiatry at the University of Miami Miller School of Medicine.

A second study -- led this time by Dr. Nora D. Volkow, director of the U.S. National Institute on Drug Abuse -- suggests that the ADHD drug Ritalin works by increasing the brain's production of dopamine.

This finding implies that reduced production of dopamine is involved in ADHD and may help explain why many people with the condition also abuse drugs.

"Individuals with ADHD have a decreased function of the brain dopamine system," Volkow said. "ADHD, clearly, is associated with a biochemical dysfunction," she added.

The finding is important, because it belies the myth that ADHD is not a real disease but was just created "to sell medication," Volkow said. Instead, "this finding explains why stimulant medications, such as Ritalin, are beneficial, because they increase dopamine function in the brain," she said.

In the study, Volkow's team performed brain scans of 19 adults with ADHD who had never received Ritalin, as well as 24 healthy individuals. The scans were done after the participants were given shots of Ritalin or placebo.

The team found that the people with ADHD released less dopamine into their blood than those without the disease. However, Ritalin caused less of a decrease in dopamine than usual in these individuals. This reduction in dopamine was associated with typical symptoms of inattention, the researchers found.

Volkow noted that drugs such as nicotine, cocaine and methamphetamine also improve dopamine brain function.

"This may be the reason why individuals that have ADHD are at a much greater risk of abusing substances than the general population, because drugs of abuse increase dopamine brain function, and they will 'feel better,' " Volkow said.

More information

For more on ADHD, visit the U.S. National Institute of Mental Health.

SOURCES: Philip Shaw, M.D., Ph.D., researcher, Child Psychiatry Branch, U.S. National Institute of Mental Health, Bethesda, Md.; Nora D. Volkow, M.D., director, U.S. National Institute on Drug Abuse, Bethesda, Md.; Jon A. Shaw, M.D., professor and director, child and adolescent psychiatry, University of Miami Miller School of Medicine; August 2007,Archives of General Psychiatry