Omeprazole is a medicine that reduces the amount of acid in your stomach. It's used to treat conditions such as heartburn. You can buy some types from pharmacies and shops, but most types are only available with a prescription. 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. Find patient medical information for Omeprazole (Prilosec, Prilosec OTC) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Omeprazole (Prilosec) is a proton pump inhibitor that reduces stomach acid. It’s available both over the counter and with a prescription. Common omeprazole side effects include headaches and stomach-related side effects, such as nausea, vomiting, or diarrhea. Learn about the side effects of omeprazole, from common to rare, for consumers and healthcare professionals. 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] 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. Omeprazole is a proton pump inhibitor that is used to treat symptoms of gastroesophageal reflux disease and other conditions caused by excess stomach acid. 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). Omeprazole belongs to a group of medicines known as proton pump inhibitors, or PPIs, and is commonly used across the UK to treat conditions such as heartburn, stomach ulcers, and gastro-oesophageal reflux disease.