Omeprazole reduces the amount of acid your stomach makes. It's a widely used treatment for indigestion and heartburn and acid reflux. It's also taken to prevent and treat stomach ulcers.

Sometimes omeprazole is taken for a rare illness caused by a tumour in the pancreas or gut called Zollinger-Ellison syndrome.

Omeprazole comes as capsules, tablets and as a liquid that you swallow (this is made to order).

All types of omeprazole are available on prescription. You can buy the lowest strength 10mg tablets and capsules from pharmacies.

• It's usual to take omeprazole once a day in the morning.
• For severe illness, you can take it twice a day - in the morning and in the evening.
• Common side effects include headaches, diarrhoea and stomach pain. These tend to be mild and go away when you stop taking the medicine.
• If you're self-treating with omeprazole, do not take it for longer than 2 weeks without checking with a doctor.
• Omeprazole is also called by the brand names Losec and Losec MUPS.

Omeprazole can be taken by adults, including pregnant and breastfeeding women.

Omeprazole can be taken by children and babies if it's been prescribed by a doctor.

To make sure omeprazole is safe for you, tell your doctor if you:

• have had an allergic reaction to omeprazole or any other medicines in the past
• have liver problems
• are due to have an endoscopy

Ask your doctor if you should stop taking omeprazole a few weeks before your endoscopy. This is because esomeprazole may hide some of the problems that would usually be spotted during an endoscopy.

It's usual to take omeprazole once a day, first thing in the morning. It doesn't upset the stomach, so you can take it with or without food.

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

How much to take

The usual dose to treat:

• indigestion is 10mg to 20mg a day
• heartburn and acid reflux is 20mg to 40mg a day
• stomach ulcers is 20mg to 40mg a day
• Zollinger-Ellison syndrome is 20mg to 120mg a day

Doses are usually lower for children and people with liver problems.

Tablets and capsules

Each tablet or capsule contains 10mg, 20mg or 40mg of omeprazole.

Swallow tablets and capsules whole with a glass of water or juice.

If you have problems swallowing capsules, you can open some brands of omeprazole capsules and mix the granules inside with a small amount of water or fruit juice, or sprinkle them on soft food, such as yoghurt or apple puree.

Do not open capsules that have a special coating (like those made by Dexel). Talk to your pharmacist if you're not sure whether you can open your capsules.

Omeprazole also comes as a tablet that melts in your mouth.

You can buy omeprazole 10mg tablets and capsules from pharmacies.

They're the same as omeprazole 10mg tablets and capsules that you get on prescription, but they're meant to be taken only by adults, and only for up to 4 weeks.

Liquid omeprazole

Liquid omeprazole can be prescribed by a doctor and made to order for children and people who cannot swallow capsules or tablets.

It'll come with a syringe or spoon to help you take the right amount. If you don't have a syringe or spoon, ask your pharmacist for one.

Do not use a kitchen teaspoon as it will not give the right amount.

Will my dose go up or down?

Sometimes your doctor will increase your dose of omeprazole if it isn't working well enough.

Depending on the reason you take omeprazole, you may take a higher dose to begin with, usually for a month or two.

After this, your doctor may recommend that you take a lower dose.

How long will I take it for?

If you bought the medicine yourself from a pharmacy, tell your doctor if you feel no better after taking omeprazole for 2 weeks.

They may want to do tests to find out what's causing your symptoms or change you to a different medicine.

Depending on your illness or the reason you're taking omeprazole, you may only need it for a few weeks or months.

Sometimes you might need to take it for longer, even for many years.

Some people don't need to take omeprazole every day and take it only when they have symptoms.

Once you feel better (often after a few days or weeks), you can stop taking it.

But taking omeprazole in this way isn't suitable for everyone. Talk to your doctor about what's best for you.

What if I forget to take it?

• If you usually take it once a day, take the missed dose as soon as you remember, unless it's within 12 hours of your next dose, in which case skip the missed dose.
• If you usually take it twice a day, take the missed dose as soon as you remember, unless it's within 4 hours of your next dose, in which case skip the missed dose.

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

If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

It's very unlikely that taking 1 or 2 extra doses by accident will cause any problems.

But you should check with your doctor if you have taken too much and have any of these symptoms:

• flushed skin
• feeling sweaty
• a fast heartbeat
• feeling sleepy
• blurred vision
• feeling confused or agitated

Most people who take omeprazole don't have any side effects. If you do get a side effect, it's usually mild and will go away when you stop taking omeprazole.

Common side effects

Common side effects, which happen in more than 1 in 100 people, include:

• headaches
• feeling sick
• being sick (vomiting) or diarrhoea
• stomach pain
• constipation
• wind

Omeprazole may also make you feel dizzy or sleepy. Some people might find it difficult to fall asleep.

It may also cause an itchy or lumpy skin rash, or make your feet or ankles swell.

Talk to your doctor or pharmacist if the side effects bother you or don't go away.

Serious side effects

Serious side effects are rare and happen in less than 1 in 1,000 people.

Call a doctor straight away if you have:

• joint pain along with a red skin rash, especially in parts of your body exposed to the sun, such as your arms, cheeks and nose - these can be signs of a rare condition called subacute cutaneous lupus erythematosus. This can happen even if you have been taking omeprazole for a long time
• yellow skin, dark pee and tiredness - these can be signs of liver problems

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to omeprazole.

These are not all the side effects of omeprazole. For a full list, see the leaflet inside your medicines packet.

What to do about:

• headaches - make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller. Headaches should usually go away after the first week of taking omeprazole. Talk to your doctor if they last longer than a week or are severe.
• feeling sick - try taking omeprazole with or after a meal or snack. It may also help if you don't eat rich or spicy food.
• being sick (vomiting) or diarrhoea - drink plenty of water by having small frequent sips to avoid dehydration. Signs of dehydration include peeing less than usual or having strong-smelling pee. Do not take any other medicines to treat diarrhoea or vomiting without speaking to a pharmacist or doctor.
• stomach pain - try to rest and relax. It can help to eat and drink slowly and have smaller and more frequent meals. Putting a heat pad or covered hot water bottle on your stomach may also help. If you are in a lot of pain, speak to your pharmacist or doctor.
• constipation - get more fibre into your diet, such as fresh fruit and vegetables and cereals, and drink plenty of water. Try to exercise, for example, by going for a daily walk or run. If this doesn't help, talk to your pharmacist or doctor
• wind - steer clear of foods that cause wind, like pulses, lentils, beans and onions. It might also help to eat smaller and more frequent meals, eat and drink slowly, and exercise regularly. Some pharmacy remedies, such as simethicone, may relieve symptoms of wind.

Usually, omeprazole is safe to take during pregnancy and while breastfeeding.

If you're pregnant, it's always better to try to treat indigestion without taking a medicine.

Your doctor or midwife will first advise that you try to ease your symptoms by eating smaller meals more often and avoiding fatty and spicy foods.

They may also suggest raising the head of your bed 10 to 20cm by putting something under your bed or mattress, so that your chest and head are above your waist. This helps stop stomach acid travelling up towards your throat.

If lifestyle changes don't work, you may be recommended a medicine like omeprazole.

For more information about how omeprazole can affect you and your baby during pregnancy, read this leaflet on the Best Use of Medicines in Pregnancy (BUMPS) website.

Omeprazole and breastfeeding

Omeprazole is safe to take while you're breastfeeding. It passes into breast milk, but only in small amounts that aren't harmful to the baby.

But if your baby is premature or has health problems, check with your doctor first.

Some medicines and omeprazole can interfere with each other and make it more likely that you'll have side effects.

Tell your doctor if you're taking these medicines before you start omeprazole treatment:

• heart medicines, such as digoxin
• cilostazol (treats peripheral arterial disease)
• antifungal medicines, such as itraconazole, ketoconazole, posaconazole and voriconazole
• methotrexate (treats psoriasis and rheumatoid arthritis)
• HIV medicines
• phenytoin (an anti-epilepsy medicine)
• rifampicin (an antibiotic)
• bloodthinning medicines, such as clopidogrel and warfarin

These are not all the medicines that may not mix well with omeprazole. For a full list, see the leaflet inside your medicine packet.

Mixing omeprazole with herbal remedies and supplements

Do not take St John's wort, the herbal remedy for depression, while you're taking omeprazole.

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