Antibiotics don't help fight most sinus infections, although doctors routinely prescribe them for that purpose, researchers said Tuesday.
The medications are known to fuel the evolution of drug-resistant bacteria and experts have grown increasingly worried about overuse.
That's a particular concern with sinus infections, because doctors can't tell if the disease is caused by bacteria or by a virus, in which case antibiotics would be worthless.
The new study, published in the Journal of the American Medical Association, found antibiotics didn't ease patients' symptoms or get them back to work any sooner than an inactive placebo pill.
"There is not much to be gained from antibiotics," said Dr Jane Garbutt of Washington University School of Medicine in St Louis, who led the work.
"Rather than give everybody an antibiotic hoping to find the ones with bacteria, our findings would suggest refraining from antibiotics and doing what we call watchful waiting," she told Reuters Health.
That involves keeping an eye on patients to see if they get better, but not using other drugs than over-the-counter painkillers.
People with sinus infections, also called acute sinusitis, have lasting and severe cold-like symptoms such as runny nose and pain around the eyes, the nose or the forehead.
"It's the fifth most common reason antibiotics are prescribed for adults," said Garbutt. "It's hard for doctors not to give an antibiotic because patients are so miserable and we don't have anything else to give them."
But it hasn't been clear whether the drugs actually work, and even the studies that have found some benefit see the majority of placebo-treated patients get better by themselves.