ADHD Linked to Dopamine Levels

New studies shed light on the brain chemical's role in symptoms in adults with attention deficit disorder.

Monday August 13th - 8:46am

Two new studies on ADHD highlight the importance of the brain chemical dopamine in adults with attention deficit hyperactivity disorder (ADHD ADD). A team of researchers, led by Nora D. Volkow, M.D., director of the National Institutes of Health's National Institute on Drug Abuse, found levels of depressed dopamine activity in adults with ADHD, which can contribute to ADHD symptoms such as inattention.

The results also help explain how dopamine relates to substance abuse problems that are common among adults with ADHD, and why stimulant medications for attention deficit hyperactivity disorder are effective in these adults with ADHD.

In the outpatient study, researchers looked at the brain scans of 19 adults with ADHD (average age 32) who never received medication and of 24 healthy adults of similar age without ADHD; patients were given either methylphenidate or a placebo. The group of adults with ADHD had decreased dopamine activity, but when given a stimulant, were shown to have an increased concentration of dopamine and reported feeling better able to perform. It's known that people with untreated ADHD are more likely to abuse alcohol and other potentially harmful substances, and this new study helps explain why that is.

According to Dr. Volkow, "A person then has a greater risk (of substance abuse) because it's not just that they are taking the drug because they want to get high, but by taking the drug, they may actually feel better and temporarily perform better."

In a longitudinal study, led by Dr. Philip Shaw, of the National Institute of Mental Health's child psychiatry unit, researchers examined the MRIs of the brain structure of 105 children with ADHD (average age 10) and 103 children without ADHD. They found that a version of a gene involved with dopamine appeared to be linked to a diagnosis of ADHD and with regional thinning of tissue in areas of the brain that control attention.

Details of the studies are published in the August 2007 issue of the Archives of General Psychiatry.

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