NEW YORK – Medications given to children for attention deficit hyperactivity disorder (ADHD) do not appear to pose risks to their cardiovascular health over the long term, at least at low doses, according to a new study conducted in Sweden.

The researchers followed 69 children being treated with the stimulant methylphenidate for ADHD for an average of three years. The researchers saw no significant changes in the kids' blood pressure or heart rate over this period. In the United States, methylphenidate is sold under the brand names Ritalin and Methylin.

"Our impression is this is a very safe drug," said study researcher Dr. Elisabeth Fernell, of Skaraborg hospital in Sweden. However, she noted the results are preliminary, adding she and her colleagues plan to conduct further analysis. Previously, other scientists had raised concerns the stimulant might cause dangerous physiological changes in children when taken for many years.

There were some effects, however, on the children's height and weight. The children were, on average, slightly shorter than their expected height, the researchers said. And overweight children lost weight while on the drug, bringing them down to a normal body mass index, or BMI. (BMI is a ratio of weight to height, and is considered an indicator of body fatness).

The researchers said some children may have lost weight because the drug helped them control impulsive eating . "They can concentrate more, and don't eat all the time," said study researcher Dr. Ulrich Brandstetter, also of Skaraborg hospital.

Effects on children in the United States may be different because kids in this country are usually prescribed higher doses, Brandstetter said. All children should be monitored for their responses to the drugs, the researchers say.

The study was presented here on Thursday (Oct. 28) at the annual meeting of the American Academy of Child and Adolescent Psychiatry.