Researchers say healthy mice injected with the ADHD drug Ritalin show changes in the reward centers of the brain that mimic those seen in cocaine addiction. The study, funded by the National Institute on Drug Abuse, was prompted by reports that more than 7 million healthy Americans have used Ritalin and other stimulant drugs to get high or to give them an edge in academic performance. But experts point out that this study applies to Ritalin's effect on a healthy brain, and is only relevant to...