CHICAGO -- American children take anti-psychotic medicines at about six times the rate of children in the United Kingdom, according to a comparison based on a new U.K. study.

Does it mean U.S. kids are being overtreated? Or that U.K. children are being undertreated?

Experts say that's almost beside the point, because use is rising on both sides of the Atlantic. And with scant long-term safety data, it's likely the drugs are being over-prescribed for both U.S. and U.K. children, research suggests.

Among the most commonly used drugs were those to treat autism and hyperactivity.

In the U.K. study, anti-psychotics were prescribed for 595 children at a rate of less than four per 10,000 children in 1992. By 2005, 2,917 children were prescribed the drugs at a rate of seven per 10,000 -- a near-doubling, said lead author Fariz Rani, a researcher at the University of London's pharmacy school.

The study is being released today in the May edition of the journal Pediatrics.

By contrast, an earlier U.S. study found that nearly 45 American children out of 10,000 used the drugs in 2001 versus more than 23 per 10,000 in 1996.

There are differences that could help explain the vastly higher U.S. rate. A recent report in The Lancet suggested that the U.K.'s universal health care system limits prescribing practices there. The report also said direct-to-consumer ads are more common in the United States. These ads raise consumer awareness and demand for medication.

Vanderbilt University researcher Wayne Ray said U.K. physicians generally are more conservative about prescribing psychiatric drugs. Ray co-authored the U.S. study, published in 2004.

Dr. William Cooper, a Vanderbilt pediatrician, said the study shows the drugs are being used "without full understanding about the risks."