What are antibiotics?

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

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 coldsflu, 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’.

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.

You can report any suspected side effects to the Health Products Regulatory Authority (HPRA).

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.

Antibiotic resistance means that some antibiotics that used to work well for some infections, do not work anymore. It’s a big problem.

There are strains of bacteria that are resistant to antibiotics. They’re known as ‘superbugs’.

A few things cause antibiotic resistance. They include the overuse of antibiotics. This is why antibiotics should not be used to treat some viral infections, including some chest and many ear infections.

Causes of antibiotics resistance

Antibiotic resistance is caused by:

• overuse of antibiotics – the more times a bacteria comes in to contact with an antibiotic the more likely it is that the bacteria will find ways to change itself and survive

• bacteria growing, changing and spreading very fast – this means some antibiotics will no longer work properly for certain infections

• antibiotics killing our ‘good’ bacteria as well as our ‘bad’ bacteria – this means superbugs can grow and take over

Superbugs and antibiotic resistance

Superbugs are strains of bacteria that have developed resistance to many different types of antibiotics.

They are becoming an increasing cause of disability and death across the world.

MRSA and CPE are 2 kinds of superbugs.

The spread of superbugs is a problem because:
• they spread easily to others – in particular to people taking antibiotics
• it can be hard to find a safe and effective antibiotic to fight a superbug infection
• there is a risk that new superbugs may develop that cannot be treated by any existing antibiotics

How to slow antibiotic resistance

We can help to slow down antibiotic resistance by:
• not asking for antibiotics to treat viral infections, including colds and flu
• only taking antibiotics when your GP or prescriber thinks you need them
cleaning your hands regularly and keeping toilets clean – this makes it harder for superbugs to spread.

Using antibiotics in the right way will help them remain effective.