Acid reflux and heartburn, inflammation of the food pipe, stomach and duodenal ulcers, protection against ulcers caused by NSAIDs, part of the treatment that clears Helicobacter pylori, and rare acid-overproducing conditions such as Zollinger-Ellison syndrome.

Acid is pumped into the stomach by proton pumps on its lining cells. Omeprazole is activated in the acid itself and then locks onto those pumps permanently, so each one is out of action until the cell builds a new one. Acid output falls sharply for a day or more, which lets inflamed tissue and ulcers heal.

Headache, diarrhoea or constipation, wind, nausea and stomach pain. Most are mild and settle.

Take it at least half an hour before food, usually before breakfast. Long-term use is linked to low magnesium and vitamin B12, a higher risk of gut infections, and a small increase in fracture risk, so it is reviewed rather than repeated indefinitely. Tell your doctor about liver disease, and about difficulty swallowing, vomiting blood, black stools or unexplained weight loss, which need investigation rather than acid suppression. Some strengths are sold without a prescription in Pakistan.