"About one-third of individuals with physician-diagnosed asthma did not have asthma," said the study published in the Canadian Medical Association Journal (CMAJ).
"This finding suggests that, in developed countries such as Canada, asthma is over-diagnosed."
Thus, millions of people worldwide may be taking costly medications and making life changes needlessly to treat the chronic respiratory disorder in which airways suddenly constrict in response to allergens, cold air, exercise, or emotional stress.
Between 1980 and 1994, the prevalence of asthma increased by 75 percent in Canada and the United States.
In 2005, 8.3 percent of Canadians aged 12 or older were identified as having asthma, said Statistics Canada. And in 2007, 3.4 million prescriptions were issued for the top asthma medications, at a total cost of nearly 329 million Canadian dollars (268 million US), according to IMS Health Canada.
Globally, the latest data indicates 300 million people have asthma and the figure is projected to rise to 400 million cases by 2025.
The Canadian researchers said the higher prevalence of both symptoms and diagnoses of late may be due to increased awareness of the disorder, stemming in part from the pharmaceutical industry's advertising of new asthma medications.
The Canadian study looked at 540 individuals diagnosed with asthma, putting them through a battery of tests that showed a third of them actually did not have the disorder.
Based on its findings, researchers estimated that less than half of Canadians diagnosed with asthma underwent a test used to measure lung function, called spirometry.
The test is said to be one of the most efficient ways to diagnose asthma and other pulmonary diseases, but it is costly and time consuming.
This lack of proper testing is "unacceptable," said CMAJ deputy editor Matthew Stanbrook and Alan Kaplan of the Family Physician Airways Group of Canada, in an editorial on the Canadian Medical Association Journal's website.
"A physician who attempted to manage hypertension without measuring blood pressure or to manage hypercholesterolemia without measuring serum cholesterol levels would not be considered to be maintaining an adequate standard of care," they said.
"Treating asthma without having performed at least spirometry is no different."
Some inhaled steroids used to control the symptoms of asthma, doctors note, have been linked to cataracts, glaucoma and osteoporosis.
Also, Health Canada has warned of the possible increased risk of death associated with use of some asthma medications.