Chicago ? A new analysis suggests there’s been a huge increase in the number of U.S. children diagnosed with bipolar disorder, but experts question whether the surge is real and say some kids have been mislabeled.

Researchers looked at the number of times children under 19 went to the doctor and were diagnosed with or treated for bipolar disorder, also known as manic depression. They found a 40-fold increase, from an estimated 20,000 visits in 1994 to 800,000 in 2003. The jump coincided with children’s rising use of antipsychotic medicine.

The numbers echo other estimates suggesting as many as 1 million U.S. children are bipolar, but it remains a controversial diagnosis in children. That’s partly because their symptoms often differ from adults’ and because most powerful antipsychotic drugs used to treat bipolar disorder were approved for adults and have not been well-studied in children.

Some doctors believe bipolar disorder doesn’t occur in children, and until last month there was only one drug approved to treat the illness in kids.