Brain chemical has key role in ADHD: studies

By Will Dunham

WASHINGTON (Reuters) - Two studies published on Monday showed the importance of a brain chemical in attention deficit hyperactivity disorder, with researchers saying it might help explain why people with ADHD often are substance abusers.

Researchers at the U.S. National Institutes of Health focused on the role of dopamine, a chemical messenger in the brain involved in governing movement, emotional response and the ability to feel pleasure and pain.

A team led by Dr. Nora Volkow, director of the NIH's National Institute on Drug Abuse, documented decreased dopamine activity in the brains of a group of adults with ADHD. Volkow said the decreased dopamine activity related to systems involved with attention and cognition, but also with reward.

Researchers have known that people with ADHD are more likely than others to smoke cigarettes and abuse alcohol, marijuana, cocaine and other drugs. The decreased dopamine activity in the brains of people with ADHD pointed to an explanation, Volkow said.

"If you take a drug of abuse, whether it's alcohol, nicotine or cocaine or methamphetamine -- it doesn't matter -- what you're going to be doing is temporarily increasing the concentration of dopamine in the brain," Volkow said in a telephone interview.

"So 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."

ADHD is a condition that often becomes apparent in preschool and early school years. Children with ADHD have a tougher time controlling their behavior and paying attention.

The usual treatment for ADHD may include drugs like Ritalin, or methylphenidate, a stimulant intended to lower impulsiveness and hyperactivity and boost attention. Volkow said the study may explain how such stimulant drugs work in people with ADHD -- by amplifying dopamine in the brain.