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Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or stopping them from growing. 

Antibiotics are usually prescribed as tablets or capsules that you swallow.

But they can also come as:

  • liquid drinks
  • sprays
  • creams
  • lotions
  • drops
  • injections

Take your GP's advice on when to use antibiotics. Antibiotics do not work for viral infections.

Do not take antibiotics if you do not need to

Taking antibiotics when you do not need them can mean they will not work for you in the future. This is known as 'antibiotic resistance'. It is a big problem.

Severe allergic reaction

A severe allergic reaction to antibiotics is rare.

Emergency action required: Call 112 or 999 if you have taken antibiotics and develop:

  • wheezing
  • breathing difficulties
  • clammy skin
  • hives

You may need to go to hospital.

Uses for antibiotics

Antibiotics are used to treat serious bacterial infections that:

  • are unlikely to clear up without medicine
  • could infect others if untreated
  • last a long time if not treated with antibiotics
  • may cause complications

They may also be recommended for people who are more vulnerable to the harmful effects of infection. For example, babies, older people, or people with certain medical conditions.

In some cases, GPs will prescribe antibiotics if they think you're at risk of getting a bacterial infection. This is called prophylaxis.

For example, you may be prescribed antibiotics before an operation to reduce the chances of you getting an infection from the operation.

When not to take antibiotics

Antibiotics do not work for viral infections such as colds, flu, and most coughs and sore throats.

Many mild bacterial infections get better on their own without using antibiotics. 

If you take antibiotics when you do not need them, they may not work as well for you in the future.

This is because there are some types of bacteria that are resistant to antibiotics. They are known as 'superbugs'.

Find out more about antibiotic resistance

Check if you can take antibiotics

Antibiotics can be taken by adults and children.

Emergency action required: Check with a GP or pharmacist before taking antibiotics if you:

  • are taking other medicines - some antibiotics do not mix well with other medicines
  • already have a medical condition - some antibiotics may not be suitable for you
  • had an allergic reaction to medicine in the past
  • are trying to get pregnant, already pregnant or breastfeeding
  • are taking the contraceptive pill

Pregnant or breastfeeding

Not all antibiotics are safe for you and your baby.

Talk to your GP or prescriber before taking an antibiotic if you're pregnant or breastfeeding. They'll prescribe an antibiotic that is safe for you and your baby.

They will ask you:

  • about the kind of infection you have
  • if you are taking other medicines
  • your stage in pregnancy
  • if you have other illnesses

If you're pregnant or breastfeeding and think you have side effects from antibiotics, talk to your GP or pharmacist.

Contraceptive pill

Some antibiotics may not mix well with the contraceptive pill.

Side effects from antibiotics can include vomiting (being sick) and diarrhoea. If you get these side effects while taking antibiotics and the contraceptive pill, use another form of contraception.

How and when to take antibiotics

Your GP or pharmacist will tell you when and how to take your antibiotics. If you're not sure, ask them or read the advice on the packet or information leaflet.

Some antibiotics need to be taken on an empty stomach and some have to be taken with food. Take your dose exactly as prescribed.

Only take antibiotics prescribed to you. Never borrow antibiotics.

It's best not to drink alcohol when you're taking antibiotics. Alcohol can make antibiotic side effects worse. Some antibiotics can cause serious side effects when mixed with alcohol.

Ask your GP or pharmacist if you can drink alcohol while you're taking antibiotics.

If you forget to take a dose

If you forget to take a dose of your antibiotics, take it as soon as you remember. Take the rest of your antibiotics as normal.

If it's almost time for the next dose, skip the missed dose. Do not take a double dose.

Take the rest of your antibiotics as normal.

If you take too much

There is a bigger risk of side effects if you take too many antibiotics or take doses closer together than recommended.

These side effects can include:

  • tummy pain
  • feeling sick (nausea)
  • being sick (vomiting)
  • diarrhoea

If you take 1 or more extra doses by mistake or have side effects, call your GP or pharmacist.

Unused antibiotics

Finish your course of antibiotics to get rid of the infection completely. Do this even if you feel better before the course of antibiotics runs out.

If you want to stop taking your antibiotics, talk to your GP or pharmacist.

Do not keep any leftover antibiotics. If you have some left over, check with your pharmacy to see if they can dispose of them.

Never give antibiotics to friends, family or pets.

Side effects of antibiotics

Antibiotics can cause side effects.

The most common side effects are:

  • feeling sick (nausea)
  • being sick (vomiting)
  • bloating and indigestion
  • tummy pain
  • loss of appetite
  • diarrhoea
  • skin rash

These are usually mild and should pass when you finish your course of treatment.

Talk to your GP, pharmacist or prescriber if you have a severe case of any side effect, or a side effect that lasts for a long time.

Read the patient information leaflet that comes with your medicine for a full list of side effects.

Non-urgent advice: Find your patient information leaflet

Your patient information leaflet is the leaflet that comes with your medicine. You can find a digital version of the leaflet online.

Report side effects

You can report any suspected side effects to the the Health Products Regulatory Authority (HPRA): report an issue -

Allergic reactions

Some antibiotics can cause mild allergic reactions.

If you've had an allergic reaction to an antibiotic, do not take that antibiotic again. Tell your GP or pharmacist.

Mild to moderate allergic reactions can usually be successfully treated by taking antihistamines. If you're concerned, call your GP.

Antibiotics can also cause severe allergic reactions.


Some people get thrush (candida) of the mouth or vagina after taking antibiotics.

This is because antibiotics can kill your body’s ‘good’ bacteria, along with the 'bad' bacteria. Our good bacteria normally stop fungal infections like thrush from happening.

Talk to your GP or pharmacist if your mouth or vagina gets sore or has a white coating while you are on antibiotics.


Antibiotics can cause a type of diarrhoea called C. diff (Clostridioides difficile). In most cases, this is mild but it can be severe.

If you have diarrhoea while taking an antibiotic talk to your GP, nurse or prescriber.

Light sensitivity

Some antibiotics can make your skin sensitive to light. Talk to your GP or prescriber if you have this side effect.

Severe aches and pains

In rare cases, some antibiotics can cause long-lasting or permanent side effects. They can impact your joints, muscles and nervous system.

Talk to your GP if you have tingling, numbness or pain in tendons, muscles or joints.

Taking antibiotics with other medicines

Some antibiotics do not mix well with other medicines. Tell your GP or pharmacist if you're taking other medicines.

Ask them if the antibiotic is safe to take with your other medicine. Your GP may not know all the medicines you're taking.

This content was fact checked by the HSE Antimicrobial Resistance and Infection Control Team (AMRIC).

Page last reviewed: 20 August 2022
Next review due: 20 August 2025

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.