More and more U.S. children are being given drugs to fight chronic conditions such as asthma and hyperactivity, according to a study published on Monday.

From 2002 to 2005 prescriptions for medicines to treat type-2 diabetes doubled, asthma medications rose by more than 46 percent, medicines for attention-deficit hyperactivity disorder increased by more than 40 percent and prescriptions for cholesterol-lowering drugs were up by 15 percent.

The study was conducted by Emily Cox of Express Scripts Inc. in St. Louis, a manager of pharmacy insurance benefit plans, Dr. Donna Halloran of the Pediatric Research Institute in St. Louis, and Douglas Mager of the Kansas Health Institute in Topeka.

In a report published in the November issue of Pediatrics, they said the increases could mean that chronic conditions are on the rise.

But they said the trend could also reflect other factors such as changes in the way doctors prescribe drugs and better screening that identifies more chronic conditions.

In addition, the team said federal programs that encouraged research on pediatric drugs resulted in "increased data on safety and efficacy in children (that) likely provided physicians with a greater degree of confidence to prescribe (such drugs)."

The findings were based on insurance claims for 3.2 million children aged 5 to 19.