During a two-year period, nearly 300 children -- including some who were under the age of five -- were admitted to a single Detroit poison control center suffering from the effects of a Ritalin overdose. So far, medical experts have no idea of how many thousands of children may be similarly affected around the country.

More than two million American children have been diagnosed with attention-deficit/hyperactivity disorder (ADHD) and most are treated with the drug Ritalin, also known by its chemical name, methylphenidate.

According to a study published in the December 2000 issue of Archives of Pediatric and Adolescent Medicine, many of them suffer symptoms such as an accelerated heart rate, agitation and listlessness after receiving an overdose of the drug.

Dr. Suzanne R. White and colleague Christina M. Yadao of Wayne State University School of Medicine in Detroit, emphasized that overdoses of any ADHD drug are potentially fatal.

"We believe there is a potential danger," said Dr. White, "especially with more younger children getting these drugs now."

The study showed that while children ages 6 to 11 had an "unusually high" incidence of accidental overdose, those younger than age five were most likely to suffer symptoms.