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 whether you need antibiotics or not.

Do not take antibiotics if you don't need too

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.

Immediate action required: Call 112 or 999 if you have taken antibiotics and begin to 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
  • carry a risk of complications

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

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

When not to take antibiotics

Antibiotics do not work for viral infections, for example, colds and 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 strains of bacteria resistant to antibiotics have emerged. They are known as 'superbugs'.

Read more about antibiotic resistance

Check if you can take antibiotics

Antibiotics can be taken by adults and children.

Immediate action required: Check with a GP or pharmacist before starting to take 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
  • have 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, take another form of contraception.

How and when to take antibiotics

Your GP, doctor 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.

Read more about the side effects of 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 antibiotic course has run 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.

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.

Read about severe allergic reactions and what to do


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 thrush, a fungal infection, 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.

Read more about thrush


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.

Finding your patient information leaflet online

Your patient information leaflet (PIL) is the leaflet that comes in the package of your medicine.


To find your PIL online, visit the Health Products Regulatory Authority (HPRA) website

  1. In the ‘Find a medicine’ search box, enter the brand name of your medicine. A list of matching medicines appears.
  2. To the right of your medicine, select ‘PIL’. A PDF of the PIL opens in a new window.

You can also:

  1. Select the brand name of your medicine.
  2. Scroll down to the Documents section.
  3. From the Package Leaflet line, select PDF version. A PDF of the PIL opens in a new window.

If your PIL is not on the HPRA website, the European Medicines Agency (EMA) website opens in a new window when you select ‘PIL’.

You can find your PIL on the EMA website.

Finding your PIL on the EMA website

If your PIL is not on the HPRA website, you will be sent to the European Medicines Agency (EMA) website.

To find your PIL on the EMA website:

  1. In the Medicines search box, enter the brand name of your medicine and the word ‘epar’. For example: ‘Zoely epar’. A list of matching medicines appears.
  2. Select the ‘Human medicine European public assessment report (EPAR)’ for your medicine
  3. From the table of contents, select Product information.
  4. Select the EPAR – Product Information link for your medicine. A PDF opens in a new window. The PIL information is in Annex III of the PDF under ‘labelling and package leaflet’

This content was fact checked by a pharmacist, a GP, the National Medication Safety Programme (Safermeds) and the Health Products Regulatory Authority (HPRA).

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

Page last reviewed: 24 September 2021
Next review due: 24 September 2024

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