Antibiotics always involve a trade-off. On the one hand, they're wonder drugs that kill off harmful bacteria. On the other, they become less effective the more they're used, as bacteria develop resistance to the drugs. In a study published this week in the Journal of the American Medical Association, a group of Harvard researchers examined doctors' prescriptions for children with sore throats and found that antibiotics are often given when they shouldn't be.

A child's sore throat can mean many things, and most of them don't require antibiotics. "Strep throat is the only common cause of sore throat for which antibiotics are needed," says Jeffrey Linder, a doctor at Brigham and Women's Hospital in Boston and the lead author of the study. Using national statistics on doctors' visits, he found that 53 percent of children with sore throats were given antibiotics even though only 17 percent were diagnosed with strep throat.

Giving antibiotics to a child with strep can stop the bacteria from being passed on to other people and decrease the risk of complications, like sinus or ear infections or rheumatic fever. The antibiotics may also help with symptoms. But they only kill bacteria. There's no point in taking them for colds, which are caused by viruses. And while taking antibiotics for a cold probably won't hurt the child, it can create a bigger problem: The antibiotics will kill off a lot of the bacteria that normally reside in the body, leaving any resistant bugs to multiply. As this process repeats itself millions and millions of times, populations of bacteria gradually develop resistance to common antibiotics, making those drugs useless for serious disease in the future.

The study also found that doctors frequently prescribed stronger antibiotics than necessary. Although many bacteria have become resistant to penicillin since the drug's introduction in the 1940s, the bacterium that causes strep throat never has. Doctors should only prescribe amoxicillin or penicillin for strep throat unless the child is allergic, Linder says. "This whole idea of coming in and getting a strong, new antibiotic is not necessary."

Doctors aren't ignorant of the dangers of antibiotic overuse. But parents often pressure doctors to give their kids antibiotics, and it can be easier to give up and write a prescription than to sit down an upset parent and a miserable child and explain the public-health problems caused by antibiotic resistance.

Find out more information about sore throats from the National Library of Medicine (http://www.nlm.nih.gov/medlineplus/ency/article/003053.htm).