Just under 8 percent of U.S. children ages 4 to 17 had ever been diagnosed with Attention deficit hyperactivity disorder in 2003, and more than half of them are being treated with drugs, the U.S. Centers for Disease Control and Prevention reported on Thursday.

Boys are more than twice as likely to be diagnosed with ADHD than girls, especially boys from poorer families, the CDC said.

The 2003 survey is the first comprehensive analysis of precisely how many U.S. children have the disorder and how many are on medication for it, the CDC said in its Morbidity and Mortality Weekly Report.

“In 2003, approximately 7.8 percent (4.4 million) of U.S. children aged 4 to 17 years had ever had ADHD diagnosed,” according to report. Estimates had ranged from anywhere between 2 percent and 18 percent, the CDC said.

It said 2.5 million, or 56 percent, had ever taken medication for the disorder.

“ADHD diagnosis was reported approximately 2.5 times more frequently among males than females. Prevalence of reported ADHD increased with age and was significantly lower among children aged 4 to 8 years compared with children aged more than 9 years.”

For the report, the CDC experts analyzed data from the 2003 National Survey of Children’s Health.

It said more 6-year-old boys were on medication for ADHD - 4.3 percent - than girls in any age group.

“The highest rates of drug treatment for ADHD by sex and age were reported among males aged 12 years (9.3 percent) and among females aged 11 years (3.7 percent),” the CDC said.

To be diagnosed with ADHD a child must have six or more symptoms for six months including frequent failure to pay attention in schoolwork or play, frequent mistakes due to inattention to schoolwork, frequent failure to listen when spoken to directly, failure to followup on chores and forgetfulness.

“ADHD poses substantial costs both to families and society,” the CDC said.

“Health care costs associated with ADHD are conservatively estimated at $3.3 billion annually,” it added.

“Moreover, persistent and negative side effects of stimulants have been documented, including sleep disturbances, reduced appetite, and suppressed growth, which might have important health implications for the millions of children who are currently taking medication for ADHD.”

Therefore, it said, experts should keep an eye on how many children have ADHD and are being medicated for it.