Omeprazole (Losec)

How does it work?

Losec capsules, Losec MUPS tablets (MUPS = Multiple Unit Pellet System) and Losec injection all contain the active ingredient omeprazole, which is a type of medicine called a proton pump inhibitor. Omeprazole is also available without a brand name, ie as the generic medicine. Omeprazole acts in the stomach to decrease the production of stomach acid.

Proton pumps are found on cells that line the stomach and are used by these cells to produce stomach acid. Omeprazole works by inhibiting the action of the proton pumps, and this reduces the production of stomach acid.

Stomach acid is produced in the stomach as a normal part of the digestive process. Normally the linings of the stomach and duodenum (an area of the intestine directly after the stomach) are protected by a layer that resists acid attack. However, if this layer is damaged, or large amounts of stomach acid are formed, an ulcer can develop on the lining of the stomach or duodenum. This is called a peptic ulcer.

Acid produced in the stomach can also sometimes flow back into the food pipe (oesophagus). This is called gastro-oesophageal reflux, and can cause pain and a burning sensation known as heartburn. It can also irritate and damage the lining of the oesophagus, causing a condition called reflux oesophagitis.

By reducing the production of stomach acid omeprazole can be used to treat all these and other conditions.

It stops excess acid flowing back into the foodpipe and can be used to relieve heartburn symptoms associated with acid reflux. It also allows the oesophagus to heal in reflux oesophagitis.

By reducing the amount of acid in the stomach and duodenum omeprazole also allows peptic ulcers to heal, and prevents them from recurring. It also relieves the symptoms of indigestion caused by excess stomach acid.

Omeprazole can also be used to prevent and treat peptic ulcers that can occur as a side effect of non-steroidal anti-inflammatory drugs (NSAIDs), such as diclofenac. NSAIDs relieve pain and inflammation by reducing the production of substances called prostaglandins. Unfortunately, prostaglandins are also produced in the stomach and help to protect the stomach lining from acid, so NSAIDs can allow the acid to irritate the stomach. Omeprazole is used to treat peptic ulcers that occur due to this irritation. It also relieves side effects such as indigestion that can be associated with taking these medicines. Omeprazole is also sometimes prescribed in combination with NSAIDs to help prevent peptic ulcers from developing.

Omeprazole is also given together with antibiotics to help eradicate bacteria called Helicobacter pylori from the stomach. These bacteria can contribute to the formation of peptic ulcers. Omeprazole helps create an environment in the gut in which the antibiotics can be more effective at killing the bacteria.

Omeprazole is used in varying doses and for varying lengths of time depending on the condition being treated.

What is it used for?

  • Gastro-oesophageal reflux disease.
  • Indigestion symptoms such as heartburn related to excess stomach acid.
  • Peptic ulcers.
  • Eradicating bacteria in the gut (Helicobacter pylori) that cause peptic ulcers (in combination with antibiotics).
  • Preventing, treating and relieving symptoms of peptic ulcers or erosions associated with non-steroidal anti-inflammatory drugs (NSAIDs).
  • Excessive secretion of stomach acid due to a tumour or enlargement of the pancreas (Zollinger-Ellison syndrome).
  • Preventing inhalation of acid from the stomach (acid aspiration) while under general anaesthetic.

How do I take it?

  • The number of tablets or capsules to take, how often and for how long will depend on the condition being treated. It is important to follow the instructions given by your doctor. These will also be printed on the dispensing label that your pharmacist has put on the packet of medicine.
  • Omeprazole is broken down by stomach acid. For this reason, Losec capsules contain the omeprazole in pellets that have a special enteric coat to protect the omeprazole from the acid. This allows the omeprazole to pass through the stomach into the intestine where it is absorbed. Losec MUPS tablets are made up of pellets of omeprazole with a similar protective coat. Losec capsules and MUPS tablets must not be chewed, broken or crushed, as this would destroy the special coat, allowing the omeprazole to be broken down in the stomach and making it ineffective.
  • People who have difficulty swallowing Losec capsules whole can open the capsules. The pellets inside can either be swallowed directly with half a glass of water, or be suspended in 10ml of non-carbonated water, apple juice, orange juice or pineapple juice, or in apple sauce or yoghurt and swallowed after gentle mixing. This mixture should be taken immediately or within 30 minutes. Stir just before drinking and rinse it down with half a glass of water. Alternatively the actual capsules may be sucked and the pellets swallowed with half a glass of water. Do not chew or crush the pellets that are inside the capsules.
  • People who have difficulty swallowing Losec MUPS tablets can disperse the tablets in 10ml of non-carbonated water and then gently mix this in a small amount of apple, orange or pineapple juice, or in apple sauce or yoghurt. Do not use milk or carbonated water. The dispersion should be taken immediately or within 30 minutes. Stir the dispersion just before drinking and rinse it down with half a glass of water. Do not crush or chew the tablets.
  • If you forget to take a dose take it as soon as you remember. However, if it is almost time for your next dose just skip the missed dose and take your next dose as normal. Don't take a double dose to make up for a missed dose.


  • Stomach cancer can have similar symptoms to stomach ulcers, and these symptoms can be relieved by omeprazole. For this reason, if it is suspected that you have a stomach ulcer, your doctor should exclude the possibility of stomach cancer before you start treatment with this medicine. Otherwise, this medicine could mask the symptoms of stomach cancer and therefore delay diagnosis of this condition. This is particularly important if you are middle aged or older and have new or recently changed symptoms.
  • As omeprazole decreases the acidity in the stomach, it may lead to a slightly increased risk of getting stomach infections such as Salmonella and Campylobacter.
  • If you are taking a proton pump inhibitor medicine such as this one for longer than three months it may cause the level of magnesium in your blood to fall. This is more likely if you are also taking digoxin or a diuretic medicine (see end of factsheet). Symptoms of low magnesium can include fatigue, muscle spasms or twitching, convulsions, disorientation, dizziness and increased heart rate. You should tell your doctor if you experience any of these symptoms, as your level of magnesium may need to be checked and corrected.
  • Proton pump inhibitor medicines such as this one, particularly if taken in high doses for longer than a year, may slightly increase the risk of breaking a bone in your hip, wrist or spine. If you are elderly, or have osteoporosis or risk factors for getting osteoporosis, it is important to make sure that you have an adequate intake of calcium and vitamin D to avoid any problems with your bones. Your doctor may want you to take calcium and vitamin D supplements if you don't get enough in your diet. Ask your doctor for further advice.
  • In people having long-term treatment with this medicine, eg for Zollinger-Ellison syndrome, the medicine may reduce the absorption of vitamin B12 (cyanocobalamin) from the gut into the bloodstream. Ask your doctor for more information or advice about this.

Use with caution in

  • Decreased liver function.
  • People with osteoporosis or who are at risk of osteoporosis, for example people taking long-term corticosteroid medicines and women who have passed the menopause. (This medicine may increase the risk of breaking a bone - see the warning section above.)
  • Vitamin B12 deficiency.

Not to be used in

  • Allergy to any ingredients.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • This medicine is not known to be harmful when used during pregnancy and can be used during pregnancy. Seek further medical advice from your doctor.
  • This medicine passes into breast milk, but when taken at normal doses it is unlikely to have any harmful effects on a nursing infant. Seek further medical advice from your doctor.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.

Common (affect between 1 in 10 and 1 in 100 people)

  • Headache.
  • Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting, abdominal pain or wind (flatulence).

Uncommon (affect between 1 in 100 and 1 in 1000 people)

  • Dizziness or spinning sensation.
  • Sleepiness.
  • Difficulty sleeping (insomnia).
  • Pins and needles sensations (paraesthesia).
  • Increased liver enzymes.
  • Skin reactions such as rash, hives, itching or dermatitis.
  • Feeling generally unwell (malaise).
  • Swelling of the legs and ankles due to excess fluid retention (peripheral oedema).
  • Fracture of the hip, wrist or spine (see warning section above).

Rare (affect between 1 in 1000 and 1 in 10,000 people)

  • Blurred vision.
  • Dry mouth.
  • Taste disturbances.
  • Inflammation of the mouth (stomatitis).
  • Thrush infection (candidiasis) in the stomach or intestines.
  • Pain in the muscles and joints.
  • Confusion.
  • Agitation.
  • Depression.
  • Hair loss.
  • Increased sweating.
  • Increased sensitivity of the skin to UV light (photosensitivity).
  • Decreased numbers of white blood cells or platelets in the blood (leucopenia or thrombocytopenia).
  • Decreased level of sodium in the blood (hyponatraemia).
  • Inflammation of the liver (hepatitis).
  • Jaundice.
  • Kidney inflammation (interstitial nephritis).

Very rare (affect less than 1 in 10,000 people) or frequency unknown

  • Aggression.
  • Hallucinations.
  • Decreased level of magnesium in the blood (hypomagnesaemia) - see warning section above.
  • Liver failure.
  • Muscle weakness.
  • Severe skin reactions.
  • Breast swelling in men.
  • Impotence.

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

You should tell your doctor or pharmacist what medicines you are taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. This is particularly important if you taking any of the medicines mentioned below, because your doctor may need to monitor your treatment or alter your medicine doses. Similarly, you should check with your doctor or pharmacist before taking any new medicines during treatment with this one, to make sure that the combination is safe.

Omeprazole should not be taken by people taking the anti-HIV medicines atazanavir, nelfinavir or rilpivirine. This is because omeprazole decreases the blood level of these medicines and could make them less effective at treating HIV infection.

Omeprazole may increase the blood levels of the following medicines and may therefore increase the risk of their side effects:

  • benzodiazepines such as diazepam, triazolam, lorazepam or flurazepam
  • cilostazol (omeprazole should be avoided in people taking cilostazol)
  • citalopram
  • digoxin
  • escitalopram
  • methotrexate
  • phenytoin
  • raltegravir (omeprazole should be avoided in people taking raltegravir)
  • saquinavir (omeprazole should be avoided in people taking saquinavir)
  • tacrolimus.

Omeprazole may increase the anti-blood-clotting effect of the anticoagulant medicine warfarin. If you are taking warfarin it is recommended that your blood clotting time (INR) is checked after starting and stopping this medicine.

Due to its effect on the acidity in the stomach, omeprazole may reduce the absorption of the following medicines from the stomach, which could make them less effective:

  • erlotinib
  • itraconazole
  • ketoconazole
  • lapatinib
  • pazopanib
  • posaconazole
  • ulipristal
  • vandetanib.

The antidepressant fluvoxamine may increase the amount of omeprazole in the blood. Your doctor may prescribe you a lower than normal dose of omeprazole if you are also taking this antidepressant and seem to be getting a lot of omeprazole side effects.

Voriconazole may increase the blood level of omeprazole and omeprazole may increase the blood level of voriconazole. Your doctor may need to adjust your doses of these medicines if you are having long-term treatment with both of these medicines, or if you have severe liver problems.

The anti-HIV medicine tipranavir may reduce the amount of omeprazole in the blood and could make it less effective.

There may be a greater chance of the level of magnesium in your blood falling too low if you are taking this medicine with digoxin, diuretics (such as bendroflumethiazide or furosemide) or other medicines that can lower blood magnesium levels. If you are taking one of these your doctor may want you to have a blood test to check your magnesium levels before you start taking omeprazole and then regularly during treatment.

Omeprazole is not recommended for people taking the antiplatelet medicine clopidogrel. This is because recent evidence has shown that omeprazole can make the clopidogrel less effective at preventing heart attacks and strokes. If you are currently taking this medicine in combination with clopidogrel, you should consult your doctor to discuss this. This medicine should only be used in combination with clopidogrel if your doctor feels it is essential.

Other medicines containing the same active ingredient

Mepradec Zanprol

Omeprazole capsules and tablets are also available without a brand name, ie as the generic medicine. NB. Generic omeprazole tablets are different from Losec MUPS tablets in that the entire tablet has a special enteric coating. This means that the tablets must be swallowed whole. They cannot be dispersed in the same way as Losec MUPS tablets for people who have difficulty swallowing.