Antibiotics treat certain infections caused by bacteria. Antivirals treat some infections caused by viruses. Antibiotics do not work on viruses at all, which is why they will not help a cold or the flu.
Bacteria and viruses are different kinds of germs, so a medicine for one does not work on the other. A healthcare professional can tell you which, if any, you need.
What antibiotics do
MedlinePlus says antibiotics fight bacterial infections by killing the bacteria or making it hard for them to grow and multiply. The CDC gives strep throat, whooping cough and urinary tract infections as examples of infections they can treat.
They are not needed for everything bacterial. The CDC says many sinus infections and some ear infections can get better without them, and the NHS says many mild bacterial infections clear up on their own.
What antivirals do
Viruses cause illnesses such as the common cold, flu, COVID-19 and HIV. MedlinePlus says that for most viral infections, treatment can only help with symptoms while your immune system fights the virus. There are antiviral medicines for some viral infections.
Common illnesses and which germ causes them
| Illness | Usually caused by | Will antibiotics help? |
|---|---|---|
| Cold, runny nose | Virus | No, even if the mucus is thick, yellow or green |
| Flu | Virus | No |
| Most sore throats | Virus | No, except strep throat |
| Most chest colds (bronchitis) | Virus | No |
| Strep throat | Bacteria | Yes, a healthcare professional can confirm |
| Urinary tract infection | Bacteria | Yes, a healthcare professional can confirm |
Why it matters
The NHS calls antibiotic resistance a big problem: taking antibiotics when you do not need them can mean they will not work for you in the future. The CDC adds that their side effects can still cause harm when they are not helping.
If you are prescribed either one
- Take it exactly as prescribed. That is the CDC's advice for antibiotics, and your label or leaflet has the details for any medicine.
- Do not share it or save it for later. The CDC warns that using the wrong medicine for a future illness may delay the right treatment.
- Do not use one prescribed for someone else.
- Check the leaflet if you miss a dose, and ask your pharmacist if you are not sure. Do not take a double dose to make up for it.
A course with several doses a day is easy to lose track of, especially when you start to feel better. It helps to track each dose so you are not guessing.
Frequently asked questions
Do antibiotics work on the flu?
No. The flu is caused by a virus, and antibiotics do not work on viruses.
Does green mucus mean I need antibiotics?
Not on its own. The CDC says colds and runny noses are viral even if the mucus is thick, yellow or green.
Can I keep leftover antibiotics for next time?
The CDC says not to save them for later. Ask your pharmacy how to dispose of any you have left.
Sources
Healthy habits: antibiotic do's and don'ts, CDC. Antibiotics and Viral infections, MedlinePlus. Antibiotics, NHS.
Cadence is a free medication reminder app for iPhone and Apple Watch. It is not medical software and does not give medical advice. Cadence Pro is a one-time purchase, with no subscription.
