Losec (Omeprazole): Uses, Safety and Drug Interactions

What is Losec?

Losec 20 mg contains omeprazole, an acid-reducing proton pump inhibitor. This summary uses the UK hard gastro-resistant capsule label. Omeprazole also comes in other formulations, including tablets and liquids; their instructions are not automatically interchangeable. The purpose and duration of treatment depend on the condition being treated, not simply the strength printed on the pack.

The reviewed label covers reflux disease, stomach and duodenal ulcers, prevention of certain ulcer recurrences, and ulcers associated with nonsteroidal anti-inflammatory medicines. H. pylori treatment requires selected antibiotics alongside omeprazole. Specialist indications include Zollinger-Ellison syndrome. Paediatric treatment has specific age, weight and indication requirements.

Practical points and common effects

The capsule contains protected pellets. They must not be chewed or crushed. People who cannot swallow a capsule should ask a pharmacist about the exact leaflet instructions or another suitable formulation. Do not assume that all omeprazole products can be prepared in the same way.

Headache, stomach pain, nausea, vomiting, constipation, diarrhoea and wind are common reported effects. Dizziness or visual disturbance can make driving unsafe. Alcohol can aggravate acid symptoms. Persistent or changing symptoms need assessment, even when acid treatment temporarily helps.

When should a clinician review treatment?

Unexplained weight loss, difficulty swallowing, repeated vomiting, vomiting blood or black stools are warning signs. Omeprazole can mask symptoms of serious stomach disease. Tell the team arranging a gastroscopy or other relevant test that you take it; the team should provide any preparation instructions.

Longer treatment may require review for magnesium or vitamin B12 deficiency and bone health. Severe allergy, a blistering rash or symptoms suggesting kidney inflammation need prompt medical attention. These uncommon risks do not mean that everyone needs routine tests; monitoring depends on personal risk and treatment duration.

Interactions, pregnancy and breastfeeding

The UK label prohibits nelfinavir with omeprazole and discourages clopidogrel co-use as a precaution. Warfarin, digoxin, phenytoin, diazepam, tacrolimus, high-dose methotrexate and St John's wort are important medicines or remedies to disclose. A pharmacist should check the complete list, including nonprescription acid treatments.

UK product and NHS information allow omeprazole during pregnancy when appropriate and generally consider therapeutic use compatible with breastfeeding. Ask a clinician or pharmacist to confirm suitability for the actual product and circumstances.

Sources

• Losec 20 mg hard gastro-resistant capsules — UK SmPC — Text revised 12 February 2026; emc updated 24 February 2026
• NHS — Omeprazole — Reviewed 17 September 2025

Source check: 30 October 2026. This records a check of the cited sources, not a clinical review by a doctor or pharmacist. Product instructions and approved uses can differ between countries. Follow the leaflet supplied with your medicine and obtain personal advice from a qualified healthcare professional.