Roughly one in 25 U.S. children and adolescents is taking medication for ADHD, the researchers found.

They used an international pharmaceutical database to examine data from nearly 70 countries. In 1993, 31 countries used ADHD drugs, but by 2003 that number had risen to 55, they found.

France, Sweden, Korea and Japan all showed increases in ADHD drug use among 5- to 19-year-olds.

"The usage of ADHD medications increased 274 percent during the study period," Scheffler's team wrote in the journal Health Affairs.

The United States led the pack, accounting for 83 percent of the prescriptions and $2.4 billion in 2003. Canada and Australia also had much heavier use than the researchers predicted.

ADHD is marked by poor concentration, distractibility, hyperactivity, impulsiveness and other symptoms beyond what might be expected for the patient's age.

Amphetamine drugs can control the symptoms, but their use is sometimes controversial.

Methylphenidate, sold under the brand name Ritalin by Novartis was once the standard. But costly and long-acting medications like Johnson & Johnson's Concerta, Strattera, made by Eli Lilly and Co. and Adderral XR, made by British drugmaker Shire Plc, are now driving up costs, the researchers said.

"Costs are likely to rise globally as long-acting medications, which offer easier use and result in better compliance, become more prevalent outside the U.S.," said Dr. Peter Levine, a pediatrician with Kaiser Permanente in Walnut Creek, California.

Psychologist Stephen Hinshaw of UC Berkeley said "cross-cultural research has shown that ADHD exists in all cultures, with increased access to public education a factor in its detection."

The researchers recommended that countries keep tabs on the use of ADHD drugs and make sure their benefits are worthwhile.