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Omeprazole is used to treat indigestion and heartburn by reducing acid in your stomach.

It is also used to treat stomach ulcers and a rare illness called Zollinger-Ellison syndrome.

Omeprazole comes as capsules, tablets and as a liquid. You need a prescription to get full strength omeprazole. A low strength version is available at pharmacies.

Brand names include:

  • Losec
  • Losec Control
  • Losec MUPS

They are similar to what you get on prescription.

How omeprazole works

Omeprazole is a 'proton pump inhibitor' medicine that reduces acid in your stomach.

Proton pumps are tiny substances that make acid to digest food. Omeprazole temporarily stops these pumps working.

Get emergency help

You might need medical help if you get serious side effects, have a serious allergic reaction (anaphylaxis) or take too much.

Serious side effects

Urgent advice: Tell your GP immediately if you have:

  • joint pain and a rash on parts of your body exposed to the sun
  • yellow skin, dark pee and tiredness
  • you have skin that's red, blistering or peeling
  • lose a lot of weight without trying
  • dark pee or poo
  • severe or constant diarrhoea

Serious allergic reaction

In rare cases omeprazole can cause a serious allergic reaction.

Emergency action required: Call 112 or 999 or go to your nearest emergency department (ED) if you:

  • get a rash that's itchy, red, swollen or blistered
  • are wheezing
  • get tightness in your chest or throat
  • have trouble breathing or talking
  • have swelling in your mouth, face, lips, tongue or throat

If you take too much

Emergency action required: Go to your nearest emergency department (ED) or phone a GP if

you have taken too much omeprazole and:

  • feel dizzy or sleepy
  • see double
  • are slurring your words
  • have diarrhoea
  • pass out

Check if you can take omeprazole

Omeprazole can be taken by most adults including pregnant and breastfeeding women. But always check with your GP or pharmacist.

Children and babies can take it on prescription from your GP.

It may not be suitable if you:

  • had an allergic reaction to other medicines in the past
  • have liver problems
  • have lactose intolerance
  • are vegetarian, as capsules may contain gelatin
  • are taking nelfinavir, for HIV infection


Omeprazole can be used during pregnancy.

But talk to your GP before you start taking omeprazole if you are pregnant, think you may be pregnant or are trying to get pregnant.

It's usually better to try to treat your symptoms without taking a medicine.

Your GP or midwife may suggest eating smaller meals and avoiding fatty and spicy food. They may also suggest raising the top of your bed so that your chest and head are above your waist when you sleep.


Omeprazole passes into breast milk. But this is not likely to affect your baby if you take omeprazole the way your GP tells you to.

Your GP will decide if you can take omeprazole if you are breastfeeding.

If your baby is premature or has health problems, check with your GP before you take omeprazole.

When you start taking omeprazole

You should start to feel better within 2 to 3 days.

It may take up to 4 weeks for omeprazole to work properly. You may still have symptoms during this time.

Do not take omeprazole for longer than 14 days without checking with your GP. If you do not feel better or feel worse, talk to your GP.

How and when to take it

It's usual to take omeprazole once a day, first thing in the morning.

If you take omeprazole twice a day, take 1 dose in the morning and 1 dose in the evening.

You can take it with or without food.

Swallow tablets and capsules whole with water or juice. If you have problems swallowing, open the capsules and mix the granules with water or juice. You can also sprinkle them onto soft food.

Do not open capsules that have a special coating. Check with your pharmacist if you're not sure.

Liquid omeprazole can be made to order if you cannot swallow pills.

How much to take

The dose of your medicine depends on your condition. Your GP may increase or decrease your dose.

How long you'll need to take omeprazole

Depending on your illness, you may only take it for a few weeks or months. Some people need to take it for longer, even for many years.

If you forget to take it

If you take omeprazole once a day, take the missed dose as soon as you remember, unless it's less than 12 hours until your next dose. In that case, skip the missed dose.

If you take it twice a day, take the missed dose as soon as you remember, unless it's less than 4 hours until your next dose. In that case, skip the missed dose.

Do not take a double dose to make up for a forgotten dose.

Side effects of omeprazole

Most people who take omeprazole do not have any side effects.

If you do, they are usually mild and go away when you stop taking it.

Talk to your GP or pharmacist if side effects get worse or do not go away after a few days.

Common side effects may include:

  • headaches
  • diarrhoea
  • stomach pain
  • constipation
  • wind
  • feeling sick or vomiting
  • itchy skin rashes
  • feeling dizzy or tired
  • sore mouth or throat
  • feet or ankle swelling

See 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 -

Similar medicines

If omeprazole does not work or agree with you, your GP may suggest you try another proton pump inhibitor.

These include:

  • lansoprazole
  • esomeprazole
  • pantoprazole
  • rabeprazole

These generally work the same as omeprazole and have the same type of side effects.

Esomeprazole and pantoprazole are also available directly from pharmacies.

Long-term use

Levels of magnesium in your blood may fall if you take omeprazole for longer than 3 months.

This can make you feel tired, confused, dizzy and cause muscle twitches and an irregular heartbeat.

Taking omeprazole for more than 1 year can increase your chances of certain side effects, including:

If you get any of these symptoms, tell your GP.

If you've taken omeprazole for a long time, talk to your GP before you stop.

Taking omeprazole with other medications

Always tell your GP or pharmacist that you are on omeprazole before taking new medicines.

Tell your GP or pharmacist if you are taking, have recently taken or might take any other medicines before you take omeprazole.

In particular, tell your GP if you're taking:

  • digoxin (a heart medicine)
  • other medicines that reduce the amount of acid in your stomach
  • anti-fungals such as itraconazole, ketoconazole or posaconazole
  • methotrexate (for psoriasis and rheumatoid arthritis)
  • HIV medicines
  • phenytoin (an anti-epilepsy medicine)
  • rifampicin (an antibiotic)
  • blood thinners such as clopidogrel or warfarin
  • medicines that reduce your immune system
  • any medications for cancer
  • antidepressants

Herbal remedies and supplements

St. John's Wort may stop omeprazole working as well as it should.

Tell your pharmacist or GP if you're taking herbal remedies, vitamins or supplements.


It's safe to take painkillers such as paracetamol or ibuprofen at the same time as esomeprazole.

Talk to your GP or pharmacist or before using ibuprofen as it can upset your stomach.

Other heartburn medicines

You can take omeprazole with an antacid, for example Gaviscon.

Take it 2 hours before or after your dose of omeprazole.

Food and drink

Avoid foods that make your indigestion worse, such as spicy and fatty foods.

You should also try to limit acidic foods, caffeinated drinks and alcohol.

If you have symptoms at night, try not to eat for at least 3 hours before you go to bed.

Fact check

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