Antibiotics can be wonder drugs. Taken as prescribed, the right antibiotic can clear up a nasty bacterial infection and get you back on your feet quickly. But if you take an antibiotic when you don’t need one, you probably won’t get better any faster. And it might even make you feel worse. (Antibiotics can wipe out the "good" bacteria in your gut, which may lead to GI symptoms such as diarrhea.) More worrisome, when too many people take antibiotics they don’t need, bacteria can develop resistance to the drugs. More and more bacterial infections are becoming harder to treat for this reason.

Related: 5 Common Antibiotic Mistakes

According to the Centers for Disease Control and Prevention, illnesses that don’t normally call for antibiotics include:

  • Colds
  • Flu
  • Most coughs and bronchitis
  • Sore throats (except for those resulting from strep throat)
  • Some ear infections

Doctors prescribe antibiotics unnecessarily more often than you’d think, according to a new study from Boston University School of Medicine. "Antibiotics are definitely overused,'' says study leader Tamar Barlam, MD, director of the antimicrobial stewardship program at Boston Medical Center.

What the study found

For the study, Barlam’s team looked at the records from nearly 5,000 outpatients at Boston Medical Center who had come in to see their family doctor or internist. All complained of respiratory tract symptoms but were generally healthy otherwise. The researchers checked the medical codes for the conditions that were diagnosed and then looked to see if an antibiotic was prescribed and whether it was appropriate for the condition.

The researchers found that 45 percent of the patients got antibiotics when their condition was very likely to have been triggered by a virus rather than a bacterium. -

  • Bronchitis: 71 percent of patients with bronchitis got an antibiotic, even though the majority of bronchial infections are viral, Barlam says. One possible exception are people who have chronic bronchitis as part of another condition called chronic obstructive pulmonary disease, or COPD. In many such cases, a doctor can tell if bronchitis is viral or bacterial simply by examining the patient and observing his symptoms, without doing a lab test. Even when Barlam excluded patients with a history of COPD, 67 percent of people with bronchitis received an antibiotic.
  • Sore throat: 50 percent of patients with a sore throat got an antibiotic prescription, even though this symptom is usually caused by a viral infection. One exception is a sore throat caused by Group A streptococci bacteria. It can easily be ruled out with a lab test.
  • Colds: 28 percent of patients with a common cold were given an antibiotic prescription. "The common cold is viral," Barlam says. "No one should be getting an antibiotic for a cold." 

Younger doctors were as likely as older doctors to prescribe unneeded antibiotics. This was especially disappointing, says Barlam, since in recent years experts have tried to hammer home the proper use of these drugs.

Related: How to Avoid a Cold: A Virus Expert Reveals What Really Works

The green mucus myth

Often doctors will prescribe an antibiotic for someone who’s coughing up green mucus or sputum. "Studies have shown doctors continue to think if it's green, give antibiotics," Barlam says. But when mucus is green it’s not because an infection is bacterial — the hue is due to a gathering of pus cells in response to the invading bugs.

Family practice doctors were more likely than internists to prescribe unneeded antibiotics, Barlam found, but this isn’t a reason to ditch your family doctor for an internist. The smarter strategy is to ask the right questions if he or she wants to prescribe an antibiotic:

  • Why am I getting an antibiotic? Is my condition likely to be bacterial?
  • Are you giving me the antibiotic because you think I expect it or because you think I need it?

By taking antibiotics only when you need them, you — and the population at large — will be much better off. 

Related: 7 Ways to Ease Your Child’s Cough Without Medication

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.