Got a sore throat? Your doctor might prescribe you antibiotics. They help right? According to a new Harvard study, the answer is not always.

According to new research from Harvard-affiliated Brigham and Women’s Hospital, though only 10 percent of adults with sore throat have group A Streptococcus, or strep throat—the only cause of sore throat that antibiotics can cure—doctors prescribe antibiotics at 60 percent of sore throat visits. Despite decades of effort by the Centers of Disease Control and Prevention to cut down on inappropriate antibiotic prescribing, the rate has dropped only incrementally.

Jeffrey A. Linder, associate professor of medicine at HMS and co-author of the paper, described four common symptoms of strep throat: fever, absence of cough, tender neck glands, and swollen tonsils. Most sore throat patients show either none or just one of these symptoms, meaning that they can be treated with Tylenol and fluids and without a doctor’s visit.

Antibiotics, which target bacteria, have no positive effect on treating viral sore throats and acute bronchitis, which account for the majority of sore throat cases, according to co-author Michael L. Barnett, medical resident in internal medicine at Brigham and Women’s. In fact, antibiotics aren’t harmless; unnecessary prescription may lead to antibiotic-resistant bacteria.

“You’re taking a medicine that has no chance of helping you, and has a very real chance of hurting you,” said Linder, physician in the Division of General Medicine and Primary Care at Brigmham and Women’s.

The study, published in JAMA Internal Medicine on October 3, examined a sample of 8191 sore throat visits between 1997 and 2010, representing 92 million adult sore throat visits to primary care or emergency departments in the U.S. Research showed that sore throat visits decreased from 7.5 percent of primary care visits in 1997 to 4.3 percent in 2010.

However, the overall national antibiotic prescribing rate remained constant, as physicians continued to prescribe antibiotics at 60 percent of visits. This might be explained by habit—that doctors assume patients want antibiotics, or diagnostic uncertainty—according to Linder.

The authors of the study highlighted that though penicillin remains the most effective antibiotic for treating strep throat, it was only prescribed at 9 percent of visits. Instead, the prescription of more expensive antibiotics such as azithromycin, to which bacteria are sometimes resistant, increased from under 5 percent to 15 percent of sore throat visits.

According to the study, the cost of prescribing unnecessary antibiotics from 1997 to 2010 was conservatively $500 billion. The antibiotic prescription rate dropped from 80 percent to 70 percent around 1993, and has since plateaued at 60 percent of visits.

“This reflects the slow shift to focusing on how we can address the low-hanging fruit of overuse in medical care,” Barnett said.