Taking antibiotics for bronchitis may do more harm than good in most cases, according to researchers.

Viral infections are the cause of most bronchitis cases, while bacterial infections such as whooping cough account for only a small percentage of cases, report co-authors Dr. Richard Wenzel and Dr. Alpha Fowler.

Antibiotics are only effective against bacteria, but regardless, more than three-fourths of patients are routinely treated with a round of antibiotics for five to ten days.

Frivolous antibiotic use results in needless expense for patients, and unnecessarily exposes them to potential side effects such as diarrhea, upset stomach, rash, headaches and muscle aches.

Even worse, overuse of antibiotics leads to the development of antibiotic-resistant bacteria, and infections that are increasingly difficult to defeat, researchers caution.

Additionally, doctors almost always instruct patients to take prescription cough medicines, which have not been proven to have any medicinal effect.

Bronchitis, an inflammation of the lungs associated with a persistent cough, is a fairly common condition. About five per cent of adults see a physician for acute bronchitis each year.

Most cases will go away on their own after a few days or a week if patients rest and drink plenty of fluids, researchers note.