When I was growing up in the 1980s and '90s with two younger brothers, the antibiotic amoxicillin was a frequent guest in our house. Strep throat, sinus infections, sore throats, coughs; we all remember that thick, pink, bubble gum-flavored liquid perhaps a little too well. But this popular drug, like many antibiotics, is overprescribed—often given for illnesses that it will not help, such as viral infections. A new study shows that it is indeed no more helpful than a placebo in treating patients with a non-pneumonia lower respiratory tract infection, such as a nagging cough.

The research complements a paper published in February in JAMA, The Journal of the American Medical Association, that found that amoxicillin (know by names such as Amoxil, Alphamox, Dispermox, Trimox and others) is not effective in treating sinus infections when tested against a placebo.

For the new study, published online December 18 in The Lancet Infectious Diseases, researchers recruited 2,061 patients 18 years and older (across a dozen European countries) who went to their doctor for a lower-respiratory infection that was not suspected to be pneumonia and had a cough lasting fewer than four weeks. Half of the hackers were randomly assigned to receive amoxicillin and the other half received a placebo. Both groups were instructed to take their medication three times a day for seven days; and neither the patients nor clinicians knew which treatment was which. Participating patients received follow-up phone interviews and completed daily diary entries for symptoms (detailing, for example, cough, phlegm, runny nose, headaches, feeling unwell, etc.) as well as for side effects (including diarrhea, rashes, vomiting, etc.) for up to four weeks.

The severity or length of moderate or intense symptoms was about the same for both the antibiotic and placebo groups. And there was only a slightly higher rate of new or worsening symptoms for those patients taking a placebo (19.3 percent) than for those taking the antibiotic (15.9 percent). The findings held even in patients 60 and older, who have been thought to benefit more from antibiotic treatment for such infections.

"Patients given amoxicillin don't recover much quicker or have significantly fewer symptoms,” said Paul Little, of Primary Care and Population Sciences Division at the University of Southampton in the U.K., and co-author on the new study, in a prepared statement. "Our results show that most people get better on their own."

What's more, the study showed that more people taking the amoxicillin (which is in the penicillin family) experienced side effects such as diarrhea, rashes and/or vomiting than those taking the placebo.

The findings "should encourage physicians in primary care to refrain from antibiotic treatment in low-risk patients," said Philipp Schuetz of the Medical University Department Kantonsspital Aarau in Switzerland in a prepared statement. Schuetz wrote an essay published in the same issue of The Lancet Infectious Diseases. For the subset of patients for whom the drug appeared to have had a slight benefit, researchers could now begin looking to see what might set them—or their infections—apart. "Guidance from measurements of specific blood biomarkers of bacterial infection might help to identify the few individuals who will benefit from antibiotics despite the apparent absence of pneumonia and avoid the toxic effects and costs of those drugs," Schuetz said.

Amoxicillin is the eighth most commonly prescribed drug in the U.S., with some 52.3 million prescriptions written each year, according to the IMS research group's Institute for Healthcare Informatics' 2011 report. Its patent has expired, so generic versions of this drug have made it exceptionally affordable—often less than $25 per course even without insurance. Uncomplicated lower respiratory tract infections, such as the ones being tracked in the study, are often caused by viruses, which are not susceptible to antibiotics. But doctors are often not able to identify a virus immediately—especially in rushed and resource-strained clinical settings—leading physicians to often prescribe antibiotics as a cautionary measure.

This drug habit, however, might be doing more harm than good. "Using amoxicillin to treat respiratory infections in patients not suspected of having pneumonia is not likely to help and could be harmful," Little said. "Overuse of antibiotics—which is dominated by primary care prescribing—particularly when they are ineffective, can lead to side effects—e.g. diarrhea, rash vomiting—and the development of resistance."

The biggest hurdle might now be explaining to patients that these familiar drugs are not actually helping any better than a sugar pill would. "It is difficult to convince patients and their physicians against antibiotic use," Schuetz wrote. But the new findings should help convince everyone to think twice before starting an antibiotic prescription.

This new study also underscores the natural lengthiness of lower respiratory tract infections. A person might be infected for more than a week before showing symptoms. The severe symptoms can, themselves, last for a week, and gradually improving symptoms can linger for much longer. So in the case of these ailments, perhaps time itself is the best treatment.