The study, led by Johns Hopkins Children’s Center investigators, found that 90 percent of children with moderate to severe  ADHD continue to experience sometimes-debilitating symptoms and impairment long after their initial diagnoses and, in many cases, despite treatment.
 

The research, published online in the Journal of the American Academy of Child & Adolescent Psychiatry, is the largest and most detailed long-term analysis of preschoolers with ADHD, the Johns Hopkins investigators said.
 

“ADHD is becoming a more common diagnosis in early childhood, so understanding how the disorder progresses in this age group is critical,” said lead researcher Mark Riddle, M.D., a pediatric psychiatrist at Johns Hopkins Children’s Center. “We found that ADHD in preschoolers is a chronic and rather persistent condition, one that requires better long-term behavioral and pharmacological treatments than we currently have.”
 

The study tracked the health of 186 children and found that nine in 10 continued to struggle with ADHD symptoms six years after their original diagnosis. Those taking ADHD medication had just as severe symptoms as those who were medication-free, the study found.
 

The findings are based on detailed reports from the children’s parents and teachers from the time they were enrolled in the study, at the ages of 3 to 5 years old. The reports included information on the children’s behavior, school performance, and the frequency and severity of inattention, hyperactivity, and impulsivity.
 

The severity of the children’s symptoms did not differ significantly between the two-thirds of those taking medication and non-medicated kids, the study showed. The researchers noted it was unclear whether the lack of the medication’s effectiveness was due to poor drug choice or dosage, poor adherence, ineffectiveness, or some other reason.
 

“Our study was not designed to answer these questions,” said Riddle. “But whatever the reason may be, it is worrisome that children with ADHD, even when treated with medication, continue to experience symptoms, and what we need to find out is why that is and how we can do better.”
 

Children with oppositional defiant disorder or conduct disorder in addition to ADHD were 30 percent more likely to have persistent ADHD symptoms, compared with those whose sole diagnosis was ADHD.
 

More than 7 percent of U.S. children are currently treated for ADHD, the investigators say. The annual cost is estimated to be between $36 billion and $52 billion, according to researchers.
 

The study funded by the National Institute of Mental Health.