Antibiotics are powerful germ-fighting medicines that can help clear up some infections. But using them too often or not correctly can contribute to antibiotic resistance. This happens when bacteria change so that the antibiotics no longer work against them. Taking antibiotics when you don’t need them also increases your risk of getting an infection again later.

Antibiotic medicines kill or slow the growth of bacteria (or parasites). Some antibiotics work by damaging the bacterial cell wall; others by inhibiting or blocking the actions of enzymes involved in protein production. The type of antibiotic your healthcare professional prescribes depends on where the infection is, which types of bacteria are likely to be involved and whether the infection is serious or life-threatening.

Oral antibiotics come as tablets, capsules or liquids that you swallow. Some are also available as injections or intravenous (IV) solutions. These are usually used for severe infections or when the area of infection is difficult to reach, such as meningitis or pneumonia.

It is important to take antibiotics exactly as your doctor recommends — a complete course of treatment will ensure that the infection is fully treated and won’t recur. You should also follow your doctor’s instructions about avoiding alcohol or other medications that may interfere with the antibiotic you are prescribed. And if you have any side effects, contact your healthcare professional right away. Diarrhea, for example, is a common but usually mild side effect of many antibiotics, and it may be a sign of Clostridium difficile (C. diff) infection, which requires a different kind of medicine.