The changes in brain chemistry are known to be associated with the process of drug addiction, Kim added.
"Our results show addictive properties of methylphenidate, and imply that chronic exposure of methylphenidate in humans may lead to addiction," he said.
Kim noted that the researchers used higher doses of Ritalin than those prescribed to people. Also, taking the drug orally may not lead to addiction. But, if it's taken in high doses or injected, Ritalin could become addictive, he said.
"Indeed, methylphenidate is widely abused for improving concentration and enhancing performance, or for recreational purposes," Kim said.
But Dr. Jon A. Shaw, director of child and adolescent psychiatry at the University of Miami School of Medicine, thinks there's a greater risk of later substance abuse among children with ADHD who aren't treated with Ritalin.
"There is a lot of evidence that the use of Ritalin decreases the risk of substance abuse and cocaine use in adult life," Shaw said. "Untreated ADHD subjects are at higher risk for substance abuse and misuse of drugs in adulthood than treated ADHD [subjects]," he noted.
Shaw also noted that the mice in the study were given high doses of Ritalin. "Generalizing these findings to adults makes no sense," he said.
Shaw said he has seen only two cases of addiction to Ritalin. In both, the patients were taking higher-than-normal doses and taking them more often than prescribed.
A study published in March 2008 in the American Journal of Psychiatry found that children who are prescribed psycho-stimulants for ADHD are no more likely than their peers to abuse drugs and alcohol as young adults.
All rights reserved