New research warns on American children being six times more likely to be dosed with anti-psychotic medication than British ones are.

Scientists at the University of London’s Pharmacy School found that, in the UK, anti-psychotics were prescribed for 595 children at a rate of less than 4 per 10,000 children in 1992. Thirteen years later the number of children taking these drugs nearly doubled with 2,917 children being prescribed anti-psychotics at a rate of 7 per 10,000.

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

Although the figures still put the UK well behind the U.S., the researchers are still concerned, as the number of children being treated with anti-psychotics is on the rise in both U.S. and UK.

The UK study, involving 1992-2005 health records of more than 16,000 children, is the first large examination of these drugs in UK kids. It surprisingly found the increase was mostly in medicines that have not been officially approved for kids. The drugs were commonly prescribed for behavior and conduct disorders, which include attention deficit disorder and autism.

The report’s authors claim that side effects including weight gain, nervous system problems, and heart trouble have been reported in kids treated with anti-psychotics and there is little long-term evidence that the drugs are safe.

“This highlights the need for long-term safety investigations and ongoing clinical monitoring, particularly if the prescribing rate of these medicines continues to rise,” they said in their research.

One major concern is “whether or not the right kids are getting the most appropriate and effective treatment possible,” Dr. David Fassler, a University of Vermont psychiatry professor, who was not involved in the study, said, as quoted by the Associated Press.

The findings of the study will be published in the May edition of the journal Pediatrics.