MILWAUKEE — Kids with a broken arm do better on a simple over-the-counter painkiller than on a more powerful prescription combination that includes a narcotic, a surprising study finds.

It tested ibuprofen, sold as Advil, Motrin and other brands, against acetaminophen plus codeine — a combo called Tylenol No. 3 that is also sold in generic form.

The children on ibuprofen did better, said the study leader, Dr. Amy Drendel of the Medical College of Wisconsin in suburban Milwaukee.

"They were more likely to play, they ate better and they had fewer adverse effects," she said.

Results were published online Tuesday by the Annals of Emergency Medicine. Experts praised the study as one of the few to compare medicines that have been long used in children based on how they work in adults.

"We want to start with what's effective and less likely to cause problems," and in this case, it turned out to be a cheap, over-the-counter drug, said Dr. Knox Todd, an emergency medicine pain researcher at Beth Israel Medical Center in New York and a member of the American Pain Society's board of directors.

The results do not mean that ibuprofen beats acetaminophen for everyday pain relief in children or anyone else, though. The study tested a specific use — pain in the first three days after a broken arm — and the acetaminophen was combined with the narcotic codeine, not tested alone.

Still, it shows the best way to treat a very common problem: As many as one out of five children will break a bone before age 10 — often, an arm.

Researchers randomly assigned 336 children ages 4 to 18 to go home with liquid versions of either ibuprofen or the acetaminophen-codeine combo after being treated for a broken arm at Children's Hospital of Wisconsin. Neither the children, parents nor the doctors knew who received what treatment until the study ended.

Full results were available on 244 children. The portion who failed to get relief from their assigned medicine was roughly the same.