Brookhaven National Laboratory researchers say that children who start taking prescription medications for attention-deficit hyperactivity disorder (ADHD) young may be at higher risk for alcohol and other drug abuse later in life.

A study showed that adolescent rats given methylphenidate -- a stimulant commonly found in ADHD drugs -- had fewer dopamine receptors in their brains, which could increase their risk for drug abuse. Rats receiving the ADHD drugs also were less likely to self-administer cocaine.

"Our study shows that the brain's reward pathways are definitely influenced by methylphenidate," said lead study author Panayotis Thanos. "But the brain chemistry changes we observed suggest that the developmental stage at which treatment begins and the duration of treatment are important variables that need further study."

The study appeared online June 5, 2007 in the journal Pharmacology, Biochemistry and Behavior.