Omeprazole
Brand names: Losec, Prilosec, Omez
Proton pump inhibitor (PPI)
Omeprazole is a proton pump inhibitor (PPI) — the most effective class of drug for reducing stomach acid. It treats GERD (acid reflux), peptic ulcers, and is used to protect the stomach during NSAID therapy.
Drug Class
Proton pump inhibitor (PPI)
Category
Digestive Health
Forms Available
Capsules (10 mg, 20 mg, 40 mg), Tablets
How It Works
Omeprazole irreversibly blocks the hydrogen-potassium ATPase (the proton pump) in gastric parietal cells — the final step in acid secretion. By blocking the pump rather than histamine receptors (as H2 blockers do), PPIs suppress both basal and stimulated acid secretion by 90–95%.
What It's Used For
- Gastro-oesophageal reflux disease (GERD / heartburn)
- Peptic ulcer disease (gastric and duodenal ulcers)
- H. pylori eradication (in triple therapy with antibiotics)
- Zollinger-Ellison syndrome
- NSAID-associated gastroprotection
- Prevention of stress ulcers in critically ill patients
Available Forms
Side Effects
Common Side Effects
- Headache
- Nausea
- Diarrhoea or constipation
- Abdominal pain
- Flatulence
Serious Side Effects
- Hypomagnesaemia (low magnesium) — with prolonged use; can cause muscle cramps and arrhythmia
- Clostridium difficile infection — acid suppression alters gut microbiome
- Increased risk of community-acquired pneumonia — aspiration of less-acidic stomach contents
- Chronic kidney disease — epidemiological association with long-term PPI use
- Bone fractures — epidemiological signal with long-term use, particularly at high doses
- Vitamin B12 deficiency — impaired absorption with prolonged use
Drug Interactions
- Clopidogrel — omeprazole inhibits CYP2C19, reducing clopidogrel activation; consider pantoprazole instead
- Methotrexate — PPIs reduce renal methotrexate clearance; toxicity risk
- Atazanavir and nelfinavir — reduced absorption at raised gastric pH
- Iron and vitamin B12 — reduced absorption
When to Avoid
- Concurrent use with rilpivirine-containing HIV regimens
- Known PPI allergy (cross-reactivity between PPIs possible)
Patient Tips
- Take 30–60 minutes before the first meal for maximum efficacy — the proton pump is most active after fasting
- Swallow capsules whole; do not crush enteric-coated beads inside capsules
- PPIs are often prescribed for longer than needed — review with your doctor regularly
- If you take clopidogrel, discuss whether to switch to pantoprazole to avoid the interaction
- Lifestyle measures (weight loss, elevating head of bed, avoiding late meals) reduce reliance on PPIs
Are PPIs safe long-term?
PPIs are one of the most prescribed drug classes in the world and are generally safe for short-term use. However, long-term use (>1 year) is associated with a number of risks: hypomagnesaemia, C. difficile infection, reduced B12 and iron absorption, and epidemiological signals for kidney disease and fracture.
These risks must be weighed against the clear benefit in conditions like severe GERD, Barrett's oesophagus, and high-risk ulcer patients on NSAIDs. Regular review is recommended — many patients take PPIs indefinitely for symptoms that have resolved or could be managed with lifestyle changes.
Stopping PPIs: rebound acid hypersecretion
Stopping a PPI abruptly after long-term use can cause a rebound increase in acid secretion (worse than before treatment started) due to the upregulation of proton pumps during suppression. This often leads patients to restart the PPI, creating a cycle of dependence.
The solution is to step-down gradually (half dose, then every other day, then stop) over 4–8 weeks, combined with lifestyle changes and antacids as needed.
Medical disclaimer
This page is for educational reference only. Always follow the dosage and instructions given by your prescriber or pharmacist. Do not start, stop, or change medicines without medical advice.
Reviewed 2026-06-01 · Looms Medical Team