If you have frequent heartburn (at least twice a week), you may want to try Prilosec OTC^® (omeprazole magnesium). Prilosec OTC is an over-the-counter medication that is used to treat frequent heartburn in adults. The medication works by decreasing the production of acid in the stomach. Prilosec OTC comes in the form of a tablet and is usually taken once a day. As with any drug, there are possible side effects with Prilosec OTC, such as headaches, abdominal pain, and upper respiratory infections. Some of the factors that can affect the dose of Prilosec OTC that your healthcare provider recommends include your age, other medical conditions you may have, and other medications you may currently be taking.