Ritalin and similar medicines that millions of children and teens take to curb hyperactivity and boost attention do not raise their risk of serious heart problems, the largest safety study of these drugs concludes.

Heart attacks, strokes and sudden death were very rare and no more common in children on the drugs than in kids not taking them, the federally funded study found. That was true even for children and young adults with a higher risk of heart problems — a group doctors have long worried about when prescribing these drugs.

"This study would suggest that their risk is remarkably low. And that's good news," said the study's leader, Dr. William Cooper, a pediatrics and preventive medicine professor at Vanderbilt University.