Lansoprazole is a medication that belongs to a class of drugs known as proton pump inhibitors (PPIs). It works by reducing the amount of acid produced in the stomach, which helps treat conditions like gastroesophageal reflux disease (GERD), stomach ulcers, and Zollinger-Ellison syndrome. This medication is typically taken orally, often before meals, and is available in both prescription and over-the-counter forms. Common side effects may include headache, diarrhea, and nausea. Long-term use should be monitored by a healthcare professional due to potential risks, such as nutrient deficiencies and increased susceptibility to certain infections.