The use of drugs to treat hyperactivity in children has soared worldwide, say US researchers.
Ritalin is a mild stimulant used to treat ADHD
Between 1993 and 2003, prescriptions of ADHD medications, such as Ritalin, almost tripled.
Global spending on ADHD drugs increased nine-fold, with 83% occurring in the US, a study in Health Affairs reported.
But experts said although use of ADHD medications had increased as awareness of the disorder improved, they may still be under-used in the UK.
Use of psycho-stimulant drugs to treat attention deficit hyperactivity disorder in 5-19 year olds was examined in countries across the world.
Between 1993 and 2003 use of ADHD medications increased by 274%.
The US, Canada and Australia all had higher than expected use of the drugs.
Country-by-country analysis showed increases in other countries including France, Sweden, Korea and Japan.
In the UK, use of the drugs grew by 12.3% between 1999 and 2003 and expenditure grew by 30.8%.
Countries with traditionally low and moderate consumption of the drugs were showing moderate upswings, the researchers said.
Symptoms of ADHD include inattention, hyperactivity and impulsiveness.
In 2000, the National Institute for Clinical Excellence recommended treatment for the most severely affected children.
They estimated there are around 400,000 under 16-year olds with ADHD in England and Wales.
Monthly prescriptions for Ritalin, the standard treatment, increased from 4000 in 1994 to 359,000 in 2004.
Study leader, Professor Richard Scheffler, University of California, Berkeley, said: "ADHD could become the leading childhood disorder treated with medications across the globe.
He added that that one in 25 children and adolescents in the US is taking drugs for ADHD but the findings challenge the assumption that the disorder is a US phenomenon.
But Andrea Bilbow, chief executive of ADHD charity, ADDISS, said: "I think the rest of the world is a long way off catching up with the US.
"In the UK we are still under-diagnosing and under-prescribing."
She added that at the beginning of the study period in 1993 there was little knowledge of ADHD.
"The minute you raise awareness you're going to see an increase in diagnosis and treatment."
Dr Greg Richardson, consultant in child and adolescent psychiatry in York said there was a wide spectrum of differences in ADHD.
"If you're a bit inattentive and impulsive but can hold down a job you probably won't get a diagnosis.
"It's about where on that spectrum you can justify medication.
He added that in the UK neurodevelopmental differences were more likely to be seen as part of a spectrum of normal human behaviour than in the US.
"You need to find a balance with does the medication make the child's life easier or are you prescribing it to make life easier for the adults around them."