Omeprazole
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The medical information on this site has been reviewed by Dr. Ross Elledge (GMC registered) and is provided for educational purposes. It does not replace a face-to-face consultation with your GP or specialist. Always follow the advice of your prescribing doctor and read the patient information leaflet supplied with your medication.
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About This Medicine
Omeprazole is a proton pump inhibitor (PPI). This is a medicine that lowers the acid your stomach makes. It works by blocking the hydrogen-potassium ATPase enzyme, known as the proton pump.
This pump sits on the acid-making cells of your stomach lining. Omeprazole blocks it for good, so your stomach makes much less acid.
This strong, lasting effect cuts both your resting acid and the acid your stomach makes after eating. Doctors prescribe omeprazole for several conditions.
These include acid reflux (GORD), stomach and duodenal ulcers, Zollinger-Ellison syndrome, and ulcers caused by anti-inflammatory painkillers (NSAIDs).
It is also used to help clear a stomach germ called Helicobacter pylori. A single 20 mg dose blocks about 70% of the most acid your stomach can make.
Full effect comes after taking it once a day for 5 days. Omeprazole is one of the most prescribed medicines in the world. Lower doses are sold over the counter for short-term heartburn relief.
The BNF and NICE name PPIs as the first choice to lower acid in GORD and ulcers. If you take it for a long time, your doctor should review your treatment regularly.
Usage & Dosage
Swallow the capsules whole with a glass of water before a meal. The morning, before breakfast, works best.
The medicine binds best to proton pumps that are busy making acid, and food gets those pumps going. Do not crush, chew, or open the gastro-resistant capsules.
If you find swallowing hard, you can open a capsule. Mix the granules inside with a little acidic fruit juice or yoghurt, then swallow at once without chewing. To clear H.
pylori, take omeprazole with your prescribed antibiotics as your doctor directs. Finish the whole course, even if you feel better sooner.
If you use it long term, your prescriber should review it at least once a year.
GORD: 20 mg once daily for 4-8 weeks. To keep symptoms away, 10-20 mg daily.
Duodenal ulcer: 20 mg once daily for 4 weeks. The ulcer usually heals within 2 weeks.
Gastric ulcer: 20-40 mg once daily for 8 weeks.
H. pylori eradication: 20 mg twice daily for 7 days, with two antibiotics (for example amoxicillin and clarithromycin, as NICE advises).
Zollinger-Ellison syndrome: Start at 60 mg daily. Adjust based on how much acid the stomach makes.
NSAID prophylaxis: 20 mg once daily.
If your liver works poorly, do not take more than 20 mg daily. You do not need a different dose if your kidneys work poorly. Older patients usually do not need a changed dose.
Side Effects
Side effects are grouped by how often they happen, based on the SmPC.
Common (≥1/100 to <1/10): Headache, stomach pain, diarrhoea, constipation, wind, feeling sick, and being sick.
Uncommon (≥1/1,000 to <1/100): Dizziness, tingling or numbness (paraesthesia), trouble sleeping, dry mouth, raised liver enzymes, rash, skin inflammation (dermatitis), itching (pruritus), hives (urticaria), and feeling unwell.
Rare (≥1/10,000 to <1/1,000): A sharp drop in white blood cells (agranulocytosis), a drop in all blood cells (pancytopenia), kidney inflammation (interstitial nephritis), liver inflammation (hepatitis, with or without jaundice), serious skin reactions (Stevens-Johnson syndrome and toxic epidermal necrolysis), changes in taste, skin that reacts to sunlight (photosensitivity), joint pain (arthralgia), muscle pain (myalgia), and breast swelling in men (gynaecomastia).
Long-term use concerns (MHRA guidance): Taking a PPI for a long time (more than 1 year) is linked to low magnesium (hypomagnesaemia), a higher risk of broken bones (hip, wrist, spine), gut infection with Clostridioides difficile, low vitamin B12, and a rebound in acid when you stop.
Your doctor should weigh the risks against the benefits on a regular basis.
Warnings & Precautions
If you take a PPI long term, it should be reviewed at least once a year. The MHRA and NICE advise dropping to the lowest dose that works, or using it now and then, where you can.
Rule out stomach cancer before you start, because omeprazole can hide its symptoms. Try to avoid taking it with clopidogrel.
Omeprazole blocks the CYP2C19 enzyme and weakens how well clopidogrel stops platelets clumping. Lansoprazole or pantoprazole are better choices in this case.
Long-term PPI use lowers how much calcium your body takes in and may raise the risk of broken bones. Make sure you get enough calcium and vitamin D in your diet.
Omeprazole also affects methotrexate, slowing how the kidneys clear it, and phenytoin, raising its levels in the blood. If you take it long term, your magnesium levels should be checked.
This matters most if you also take other medicines that lower magnesium.
Contraindications
Do not take omeprazole if you are allergic to omeprazole, to similar medicines called substituted benzimidazoles, or to any other ingredient.
Do not take it with nelfinavir, because omeprazole lowers nelfinavir levels in the blood by a lot.
Take care with atazanavir, as omeprazole reduces how much your body absorbs, though this is not a complete ban.
Frequently Asked Questions
When is the best time to take omeprazole?
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Related articles: Omeprazole
Omeprazole side effects: what every patient should know
Omeprazole is generally well tolerated, but common side effects include headache, nausea, diarrhoea and abdominal pain. Long-term use carries a small increased risk of bone fractures, hypomagnesaemia and Clostridioides difficile infection. Most short-term side effects resolve within the first week of treatment.
dosageOmeprazole dosage: the right dose for your condition
For most uses, the standard adult dose of omeprazole is 20 mg once a day. A higher dose of 40 mg is used for Zollinger-Ellison syndrome, severe oesophagitis and eradication therapy. Treatment lasts from 2 to 8 weeks, depending on the condition. Always take omeprazole 30 minutes before a meal.
pregnancyOmeprazole in pregnancy: what the evidence says
Omeprazole is not known to be harmful in pregnancy, and the BNF states it can be used if clinically indicated. Large observational studies have not shown an increased risk of major birth defects. However, non-pharmacological measures and antacids should be tried first. If a PPI is needed, omeprazole has the most safety data in pregnancy.
long-termLong-term omeprazole use: risks, monitoring and safe withdrawal
Long-term omeprazole use (beyond 8 weeks) is associated with small but clinically meaningful risks including bone fractures, hypomagnesaemia, vitamin B12 deficiency and Clostridioides difficile infection. NICE recommends regular review and stepping down to the lowest effective dose. For many patients, gradual withdrawal is both possible and advisable.
nhs-infoOmeprazole: NHS prescribing information and patient guidance
Omeprazole is available on NHS prescription and over the counter at a lower dose (10 mg). It is one of the most commonly prescribed medicines in the UK, with over 30 million prescriptions annually. NICE recommends it as first-line PPI therapy for GORD, peptic ulcers and H. pylori eradication.
OverviewStopping omeprazole: how to come off it without rebound heartburn
Stopping omeprazole abruptly often causes rebound acid hypersecretion: heartburn that temporarily returns worse than before, usually for one to two weeks. Tapering gradually - halving the dose, moving to alternate days, then stepping down to antacids or alginates - makes stopping easier. People with Barrett's oesophagus or severe oesophagitis should not stop without medical advice.
OverviewOmeprazole over the counter: what you can buy in the UK and when you need a prescription
In the UK, omeprazole 20mg is available from pharmacies without a prescription as a pharmacy (P) medicine, licensed for short-term relief of heartburn and acid reflux in adults. It is intended for courses of up to 14 days at a time, with a maximum of about four weeks before seeking medical advice. Higher doses, long-term treatment and use in children remain prescription only.
OverviewOmeprazole for stomach ulcers: doses, duration and follow-up
Omeprazole heals most stomach and duodenal ulcers within 4 to 8 weeks at 20-40 mg daily. If H. pylori is found, a 7-day course of omeprazole plus two antibiotics is essential to stop the ulcer returning. Complete the full course even when symptoms settle, and seek urgent help for black stools, vomiting blood or sudden severe pain.
OverviewOmeprazole and gallstones: what it can and cannot do
Omeprazole lowers stomach acid but has no effect on gallstones, which form in the gallbladder from cholesterol or bile pigments. Because indigestion and biliary colic feel similar, gallstones are sometimes missed in people taking a PPI. If severe upper abdominal pain keeps returning despite omeprazole, ask your GP about an ultrasound scan.
OverviewOmeprazole and blood pressure: what the evidence actually shows
Omeprazole does not raise blood pressure directly, and hypertension is not a recognised side effect. Two indirect issues matter for heart patients: prolonged use can lower magnesium, especially alongside diuretics, and omeprazole weakens the antiplatelet drug clopidogrel. Review long-term use with your GP rather than stopping on your own.
Dr. Ross Elledge
Consultant Surgeon · Oral & Maxillofacial Surgery
Verified Healthcare Professional
