What is omeprazole used for?
Omeprazole (best known by the brand Losec) is the oldest and most widely used of the proton-pump inhibitors (PPIs) — the medicines that most effectively reduce stomach acid. It is used for acid reflux, heartburn, stomach and duodenal ulcers, and as part of the treatment that clears Helicobacter pylori infection.
Omeprazole is authorised in European countries on a national basis and is available both on prescription and, at a lower dose, over the counter for short-term reflux symptoms in many EU countries. The PPI class as a whole, including omeprazole, has been reviewed by the European Medicines Agency's safety committee (PRAC). This article explains how omeprazole works, how it is used, its side effects and cautions. It is informational. Whether a PPI is appropriate for you is a decision only an independent EU-registered doctor can make after reviewing your health. On Prescrivia, requests start from the omeprazole treatment page.
How omeprazole works
The stomach's parietal cells pump acid into the stomach using an enzyme called the proton pump (the H+/K+ ATPase). Omeprazole blocks this pump, sharply reducing the amount of acid produced. The effect builds over the first few days of use, rather than giving instant relief, because the pump needs to be inhibited around the clock for full effect.
Because it works at the final common step of acid production, a PPI suppresses acid more completely than the older H2 blockers (such as famotidine) or simple antacids.
The approved uses
Omeprazole is licensed for:
- Gastro-oesophageal reflux disease (GORD) — reflux, heartburn, and inflammation or erosion of the oesophagus
- Healing and prevention of stomach and duodenal ulcers
- Eradication of Helicobacter pylori (in combination with antibiotics)
- Prevention of ulcers caused by NSAID painkillers (e.g., ibuprofen, naproxen) in people at risk
The over-the-counter dose is licensed only for the short-term relief of reflux symptoms (typically up to 14 days), not for long-term self-treatment.
Dosing
| Aspect | Omeprazole |
|---|---|
| Prescription dose | 20 mg to 40 mg once daily |
| OTC dose | 20 mg once daily, short-term (up to 14 days) |
| When to take | In the morning, before food (usually 30 minutes before breakfast) |
| Onset | Full acid suppression over several days |
| Duration of action | Long (the pump stays blocked; acid recovers over days after stopping) |
Taking omeprazole before breakfast matters: the proton pumps are most active after fasting overnight, so the medicine reaches them when they are easiest to block.
Common side effects
Most people tolerate omeprazole well. The more common effects are mild:
- Headache
- Abdominal pain, nausea, bloating
- Diarrhoea or constipation
- Wind
The long-term questions the EMA looked at
Because omeprazole is so widely used — often for years — the EMA's safety committee (PRAC) has reviewed the PPI class. According to that review, the key long-term messages are:
- Low magnesium (hypomagnesaemia): long-term PPI use can lower magnesium, rarely causing muscle spasms, fatigue, or abnormal heart rhythms. Doctors may check magnesium in long-term users.
- Bone fracture risk: several years of high-dose PPI use is associated with a small increase in hip, wrist and spine fractures, probably linked to reduced calcium absorption. The lowest effective dose for the shortest needed time is advised.
- Vitamin B12: long-term use may reduce B12 absorption; relevant mainly after several years.
- Gut infections: reduced stomach acid can slightly raise the risk of gut infections such as Clostridioides difficile.
- Rebound acid: stopping a PPI abruptly after long-term use can cause a temporary surge of acid and worse reflux, so the dose is often stepped down gradually.
None of these is a reason to avoid a PPI when one is genuinely needed. They are reasons to use the lowest dose for the shortest time that controls the problem, and to review long-term use with a clinician.
The clopidogrel interaction — important for some
If you take the blood-thinner clopidogrel (after a stent or heart attack), omeprazole reduces how well clopidogrel works, because both are processed by the same liver enzyme. This is a real concern for people with heart disease. Pantoprazole is the preferred PPI for people on clopidogrel, because it does not have this interaction to the same degree. Always tell your doctor if you take clopidogrel before starting a PPI.
Important cautions
Tell your doctor if you have liver problems (the dose may need reducing), if you are due an endoscopy (a PPI can mask some findings — discuss timing), or if you take other medicines, especially clopidogrel, antiretrovirals, or medicines that depend on stomach acid for absorption (for example, ketoconazole/itraconazole). Persistent reflux symptoms that do not settle, or "red flag" symptoms (difficulty swallowing, weight loss, vomiting blood, black stools) need urgent medical assessment — not just a PPI.
Accessing omeprazole through Prescrivia
Prescrivia is a technology intermediary, not a medical provider. If you complete an online assessment about reflux or indigestion, an independent EU-registered doctor reviews your health information and decides — independently — whether a PPI such as omeprazole is appropriate, at what dose and for how long, or whether you need tests or referral first. There is no guarantee that any particular treatment will be prescribed. You can start an assessment review for omeprazole here.