Everyday Antibiotics & You
Common antibiotic side effects and when to worry
Most antibiotic side effects are mild, such as nausea or diarrhoea. A few are serious. Here is how to tell them apart and what to do.
By Dr James Okafor. Published 4 June 2026 · Clinically reviewed. This article is general information, not a substitute for advice about your own health.
Like all medicines, antibiotics can cause side effects. Most are mild and pass on their own, but a small number need urgent attention. Knowing the difference helps you use antibiotics with confidence.
Common and usually mild
Nausea, mild diarrhoea, and a loss of appetite are common. So is thrush, because antibiotics can disturb the balance of harmless bacteria and fungi in the body. These effects are unpleasant but generally not dangerous. Your pharmacist can suggest ways to manage them.
Signs that need urgent care
Seek help straight away if you notice a widespread rash, swelling of the face, lips or throat, difficulty breathing, or wheezing, which can signal a serious allergic reaction. Severe or bloody diarrhoea during or after a course can be a sign of a gut infection that needs treatment. If you have had a reaction to an antibiotic before, tell your prescriber and pharmacist so it can be recorded.
What to do
If side effects worry you, contact your prescriber or pharmacist before stopping the antibiotic on your own. For an emergency, such as trouble breathing or throat swelling, call triple zero (000).
See also antibiotics and children and the complete guide to using antibiotics safely.
General practitioner and antimicrobial stewardship lead. Reviewed 3 July 2026 · Next review due July 2027 ·View reviewer profile and credentials