Antibiotics and Antibiotic Resistance: How They Work and How to Use Them Safely

Antibiotics are medicines that kill bacteria or stop them multiplying, which gives your immune system the upper hand against a bacterial infection. They don’t work on viruses, which cause most colds, flu and COVID-19. Every time antibiotics are used, especially when they aren’t needed, bacteria have a chance to adapt and become resistant. That’s why using them carefully matters for you and for everyone else.

This article explains how antibiotics work, what antibiotic resistance is, why it matters in Australia, and practical ways you can help keep antibiotics working.

How do antibiotics work?

Bacteria are tiny living cells. Antibiotics target parts of bacterial cells that human cells don’t have, such as the bacterial cell wall or the machinery bacteria use to make proteins and copy their DNA. Depending on the type, an antibiotic either kills the bacteria outright or stops them growing so your immune system can clear the infection.

There are many different groups of antibiotics. Some work against a wide range of bacteria (broad-spectrum), while others target a narrower group. Doctors try to choose the narrowest antibiotic that will treat the likely cause of an infection, at the right dose and for the shortest effective time. This helps the medicine work while limiting side effects and resistance.

Why antibiotics don’t work on viruses

Viruses are very different from bacteria. They don’t have cell walls or their own protein-making machinery. Instead, they get inside your own cells and use them to make copies of themselves. Antibiotics have nothing to target in a virus, so they can’t shorten a cold, flu or COVID-19, and taking them for a viral illness only brings the risk of side effects. If you’re unsure whether your illness needs antibiotics, our article Do you need antibiotics? When they help and when they don’t walks through the common situations.

Side effects of antibiotics

Antibiotics are important medicines, but they aren’t harmless. As well as targeting the bacteria causing an infection, they also affect the helpful bacteria that normally live in your gut, mouth, skin and vagina. Common side effects include:

• diarrhoea, nausea or an upset stomach
• vaginal thrush or oral thrush
• skin rashes

Some people have an allergic reaction to an antibiotic. Most are mild skin reactions, but a severe allergic reaction (anaphylaxis) is a medical emergency. Always tell your doctor and pharmacist about any antibiotic allergy you’ve had in the past.

What is antibiotic resistance?

Antibiotic resistance happens when bacteria change in a way that protects them from an antibiotic, so the medicine no longer works against them. When antibiotics are used, the most sensitive bacteria die first. Any bacteria that happen to survive can multiply and pass on their resistance. The more often antibiotics are used, the more chances bacteria have to do this.

Bacteria that are resistant to several antibiotics are sometimes called “superbugs”. Infections caused by resistant bacteria can be harder to treat, may last longer, may need stronger medicines or hospital care, and can spread to other people. According to healthdirect, treatment options for some infections, such as gonorrhoea, are already becoming more limited because of resistance.

It’s the bacteria that become resistant, not you

A common misunderstanding is that your body becomes “used to” antibiotics. In fact, it’s the bacteria that change. Resistant bacteria can live in your body without causing problems, and they can be passed between people, in families, in the community and in healthcare settings. That’s why antibiotic resistance is a public health issue, not just a personal one.

Why it matters in Australia

Antibiotic resistance is recognised as a serious health threat in Australia and around the world. The Australian Government coordinates a national response, with information for the public and health professionals at amr.gov.au. A key part of that response is antimicrobial stewardship: making sure antibiotics are only prescribed when they’re likely to help, and that the right antibiotic is used, at the right dose, for the right length of time.

GPs follow national prescribing guidelines that recommend against antibiotics for illnesses that usually get better on their own, such as most colds, sore throats, coughs and many ear and sinus infections. If your doctor suggests waiting, or offers symptom relief instead of antibiotics, they’re following this advice, not cutting corners.

How you can help keep antibiotics working

• Only take antibiotics prescribed for you, for the current illness.
• Take them exactly as prescribed, including the dose, timing and how many days your doctor tells you to take them. Don’t stop early or take extra doses unless your doctor advises it.
• Never share antibiotics or take someone else’s.
• Don’t keep leftovers “just in case”. Return unused antibiotics to your pharmacy for safe disposal.
• Don’t expect antibiotics for a cold or flu. Ask your doctor what will help your symptoms instead.
• Help prevent infections by washing your hands, covering coughs and sneezes, staying home when you’re unwell and keeping up to date with recommended vaccinations.

Questions worth asking your doctor

If you’re prescribed an antibiotic, or told you don’t need one, it’s reasonable to ask:

• Is this infection likely to be bacterial or viral?
• What will happen if I wait and see?
• What side effects should I look out for?
• Does this antibiotic interact with my other medicines?
• When should I expect to feel better, and when should I come back?

To see how antibiotics fit into specific conditions such as UTIs, chest infections, earaches, sinusitis and sore throats, read Common infections: which need antibiotics and which don’t.

When to get urgent help

Call 000 or go to your nearest emergency department if you have:

• signs of a severe allergic reaction, such as swelling of the face, lips or tongue, difficulty breathing or wheezing, or feeling faint
• a high fever with confusion, drowsiness, a spreading rash or feeling very unwell
• severe pain, or redness and swelling that is spreading quickly

Contact a doctor promptly if you develop severe or bloody diarrhoea during or after a course of antibiotics, or if an infection isn’t improving as expected.

How Teldoc can help

Our AHPRA-registered GPs consult by phone or video, 7 days a week from 9 am to 7 pm (Sydney time), and most patients are seen within 15 minutes. Your doctor will ask about your symptoms and medical history, explain whether antibiotics are likely to help, and:

• prescribe treatment if clinically appropriate, with an eScript sent to your phone
• arrange tests through our pathology and radiology referrals when they would help confirm the cause
• let you know if you need to be examined in person

Telehealth suits many common infections, but not every situation. Our article What telehealth can and can’t do explains the limits. General consultations are $55 on weekdays and $75 on weekends and public holidays. See our fees page or read more about antibiotic prescriptions through Teldoc.

Frequently asked questions

Do antibiotics work against viruses?

No. Antibiotics only work against bacteria. They don’t help colds, flu or COVID-19, which are caused by viruses, and taking them for a viral illness only adds the risk of side effects.

What is antibiotic resistance?

Antibiotic resistance is when bacteria change so that an antibiotic no longer works against them. It happens more often when antibiotics are used unnecessarily, and resistant infections can be harder to treat and can spread to other people.

Can my body become resistant to antibiotics?

No. It’s the bacteria that become resistant, not your body. Resistant bacteria can live in your body and be passed on to others, which is why careful antibiotic use matters for everyone.

What should I do with leftover antibiotics?

Take them back to your pharmacy for safe disposal. Don’t keep them for a future illness or give them to someone else, as they may not be the right medicine and can contribute to resistance.

Should I stop antibiotics once I feel better?

Take your antibiotics for as long as your doctor tells you to. If you think you no longer need them or you’re having side effects, speak to your doctor or pharmacist before stopping.

This article is general health information and isn’t a substitute for advice from your own doctor. If you’re worried about your health, speak to a GP. In an emergency, call 000.

Medically reviewed by Dr Vafa Derakshan (MBBS, FRACGP), September 2026