These drugs are not effective at all against most viral infections. This is why your doctor will not always prescribe an antibiotic if you have an infection. Antibiotics should not be used for these viral infections because they don't help, they may cause side effects, and this contributes to the growing problem of bacterial resistance. Antibiotics may cause side effects. If your doctor prescribes an antibiotic, be sure to ask him or her what possible side effects to watch for.
Antibiotics can cause nausea, diarrhea, and stomach pain.
If you experience any side effects when you are taking an antibiotic, you should call your doctor. Bacteria can become resistant to an antibiotic. Bacteria can become resistant to an antibiotic that was previously effective. Resistance is most likely to develop after long-term treatment with an antibiotic or with antibiotics that kill a wide variety of bacteria. Resistance is a growing problem, and there is concern that some types of infections will eventually not be treatable with antibiotics.