TUESDAY, Feb. 3 (HealthDay News) -- Ritalin, a drug commonly used to treat children with attention-deficit hyperactivity disorder (ADHD), caused changes in the brain cells of mice similar to those seen with cocaine, a new study shows.

The researchers, from The Rockefeller University in New York City, said the findings suggest that chronic exposure to Ritalin in high doses could prove addictive, and highlight the need for more research into its long-term effects.

However, one ADHD expert said he doubted the findings were applicable to children with the condition because the doses used in the study were so high.

Indeed, in experiments with mice, the researchers found that Ritalin in doses higher than those prescribed to treat ADHD caused changes in the reward region of the brain in a way comparable to cocaine. Ritalin and cocaine are both psycho-stimulants, the researchers noted.

"Methylphenidate [Ritalin] and cocaine have similar chemical structures and their pharmacological effects appear to be similar," said study author Yong Kim, a senior research associate at The Rockefeller University.

The findings were published in this week's online issue of the Proceedings of the National Academy of Sciences.

In their experiments, Kim and his colleagues compared the effects of chronic exposure to Ritalin and cocaine in specific reward-related brain regions of mice.

Over two weeks, mice were given daily injections of Ritalin or cocaine. The researchers looked for changes in dendritic spine formation, which is related to the formation of synapses and communication between nerve cells. They also looked for levels of a protein, delta Fos B, which is associated with long-term actions of addictive drugs.

"The results indicate that chronic exposure of methylphenidate, like cocaine, changes neuronal morphology and brain chemistry, but the precise pattern observed is distinct from that of cocaine," Kim said.