Learn about the side effects of omeprazole, from common to rare, for consumers and healthcare professionals. Omeprazole is used to treat certain conditions where there is too much acid in the stomach. It is used to treat gastric and duodenal ulcers, erosive esophagitis, and gastroesophageal reflux disease (GERD). NHS information about the medicine omeprazole, including what it's used for, who can take it, how to take it and side effects. Nonprescription (over-the-counter) omeprazole is used to treat frequent heartburn (heartburn that occurs at least 2 or more days a week) in adults. Omeprazole is in a class of medications called proton-pump inhibitors. It works by decreasing the amount of acid made in the stomach. Omeprazole is a medication that treats conditions that cause too much stomach acid like heartburn, stomach ulcers and reflux disease. It works by reducing the amount of acid in your stomach. Learn about omeprazole (Prilosec) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. Omeprazole, approved by the FDA, is available as a prescription and over-the-counter (OTC) drug used as a treatment for frequent heartburn. Learn about side effects, drug interactions, dosages, warnings, and more. Overview: Omeprazole is used for heartburn, acid reflux, and other conditions where you have too much acid in your stomach. It works by reducing how much acid your stomach makes and usually takes. Omeprazole, sold under the brand names Prilosec and Losec among others, is a medication used in the treatment of gastroesophageal reflux disease (GERD), peptic ulcer disease, and Zollinger–Ellison syndrome. [1] What is omeprazole? Omeprazole is used to treat excess stomach acid in conditions such as stomach ulcers, heartburn or gastroesophageal reflux disease (GERD), active duodenal ulcer, Zollinger-Ellison syndrome and erosive esophagitis.