Losec 20mg capsules are a medication used to treat certain stomach and esophageal problems, including acid reflux, ulcers, and damage caused by gastroesophageal reflux disease (GERD). It contains the active ingredient omeprazole, which works by reducing the amount of acid produced in the stomach. The capsules should be taken orally, typically once a day before a meal, and swallowed whole with water. It is important to follow the dosage instructions provided by a healthcare professional and not to exceed the recommended dose. Possible side effects include headache, nausea, and diarrhea.