List of products in the National Drug Code with proprietary name . Ranitidine is known as an H2 blocker. It works by reducing the amount of acid in your stomach. It is used to prevent and treat heartburn and other symptoms caused by too much acid in the stomach (acid indigestion). This drug has been withdrawn from the US market due to problems with safety. A possible cancer-causing impurity has been found in some ranitidine products.