Children who suffer frequent headaches may be using far more over-the-counter pain relief medicine than parents realise and risking their health, according to a study released on Thursday.

Researchers who studied 680 children between the ages of six and 18, found more than 20 percent were overusing pain relief medicines, according to the report released at the American Headache Society annual meeting in Vancouver.

"I've been astounded by the large numbers of kids using over-the-counter medications five or six times a week, sometimes 15 to 20 times per week," David Rothner, the study's lead researcher said in a statement.

One in five children in the study overused medications, which is defined as taking more than three doses of pain relievers per week for more than six weeks, according to the study by the Cleveland Clinic in Ohio.