Experts suspect the possibility of asthma patients taking higher doses of medicine than actually required.
People with mild asthma are advised to lower their medication dose once their asthma has been brought under control but the best way to reduce the dose is not fully known.
"We need to find a way to help patients control their asthma without overmedicating them," John Mastronarde, director of the asthma centre at Ohio State University, was quoted as saying.
To control asthma, patients typically take drugs called inhaled corticosteroids to reduce inflammation in the lungs and long-acting beta agonists (LABAs) so as to open the airways.
Doctors adjust the medication dose based on the patient's symptoms and lung function.
Once a patient's asthma is controlled, the drug dose should be lowered carefully. "But that's where things just do not happen," Mastronarde said.
Once symptoms are under control, sometimes both the patient and the doctor just leave the patient on whatever they are on because they do not want it to get worse again.
Although low doses of inhaled corticosteroids are safe, taking high doses of the drugs for a long time might result in some side effects including weakening of the bones, he added in a report in LiveScience.