Antibiotics that doctors typically prescribe for sinus infections works no better than a dummy pill in getting rid of the ailment, according to a study to be published Wednesday in the Journal of the American Medical Association.

The study included 166 adults whose symptoms fit the criteria for acute sinus infection. They were randomly assigned to receive a 10-day course of either amoxicillin or placebo.

Three days after starting antibiotics, there were little difference in symptoms between those taking amoxicillin and those given a placebo. At day seven, a small improvement was seen in the antibiotic group's questionnaire scores. This modest statistical improvement disappeared by day 10, when about 80 percent of patients in both groups reported their symptoms were very much improved or cured.

"Patients don't get better faster or have fewer symptoms when they get antibiotics," says Jay Piccirillo, professor of otolaryngology at Washington University School of Medicine in St. Louis and the study's senior author. "Our results show that antibiotics aren't necessary for a basic sinus infection -- most people get better on their own."

In the United States as many as one in five antibiotic prescriptions are for sinus infections, the authors point out. And given the rise of bacteria resistant to such drugs, they say it is important to find out whether this treatment is effective. Their results show it is not.