Health Topic

Antibiotics

Used properly, antibiotics can save lives by fighting bacterial infections. Read about how to use antibiotics and about when not to use antibiotics.

Reviewed Reviewed by a registered pharmacistGeneral information

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Antibiotics

Antibiotics are medicines that fight bacterial infections in people and animals. They work by killing the bacteria or by making it hard for the bacteria to grow and multiply.

Antibiotics can be taken in different ways:

  • Orally (by mouth). This could be pills, capsules, or liquids.
  • Topically. This might be a cream, spray, or ointment that you put on your skin. It could also be eye ointment, eye drops, or ear drops.
  • Through an injection or intravenously (IV). This is usually for more serious infections.

Antibiotics only treat certain bacterial infections, such as strep throat, urinary tract infections, and E. coli.

You may not need to take antibiotics for some bacterial infections. For example, you might not need them for many sinus infections or some ear infections. Taking antibiotics when they're not needed won't help you, and they can have side effects. Your health care provider can decide the best treatment for you when you're sick. Don't ask your provider to prescribe an antibiotic for you.

Antibiotics do not work on viral infections. For example, you shouldn't take antibiotics for:

  • Colds and runny noses, even if the mucus is thick, yellow, or green
  • Most sore throats (except strep throat)
  • Flu
  • Most cases of bronchitis

The side effects of antibiotics range from minor to very severe. Some of the common side effects include:

  • Rash
  • Nausea
  • Diarrhea
  • Yeast infections

More serious side effects can include:

  • C. diff infections, which cause diarrhea that can lead to severe colon damage and sometimes even death
  • Severe and life-threatening allergic reactions
  • Antibiotic resistance infections

Call your health care provider if you develop any side effects while taking your antibiotic.

You should only take antibiotics when they are needed because they can cause side effects and can contribute to Antibiotic resistance infections. Antibiotic resistance happens when the bacteria change and become able to resist the effects of an antibiotic. This means that the bacteria continue to grow.

When you take antibiotics, it is important that you take them responsibly:

  • Always follow the directions carefully. Finish your medicine even if you feel better. If you stop taking them too soon, some bacteria may survive and re-infect you.
  • Don't save your antibiotics for later.
  • Don't share your antibiotic with others.
  • Don't take antibiotics prescribed for someone else. This may delay the best treatment for you, make you even sicker, or cause side effects.

Centers for Disease Control and Prevention

It sits within Infections and Drug Therapy.

The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Antibiotics

3,722 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Diagnosis and Tests

Related Issues

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Anti-Bacterial Agents. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Antibiotics, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.