Omeprazole 40 mg is a medication commonly used to treat conditions related to excessive stomach acid production. It belongs to a class of drugs called proton pump inhibitors (PPIs), and it works by reducing the amount of acid produced in the stomach. Omeprazole is prescribed for various gastrointestinal conditions, including gastroesophageal reflux disease (GERD), ulcers, and Zollinger-Ellison syndrome.