Rabeprazole, sold under the brand name Aciphex, among others, is a medication that decreases stomach acid. It is used to treat peptic ulcer disease, gastroesophageal reflux disease, and excess stomach acid production such as in Zollinger–Ellison syndrome. It may also be used in combination with other medications to treat Helicobacter pylori. Effectiveness is similar to other proton pump inhibitors (PPIs). It is taken by mouth. Common side effects include constipation, feeling weak, and throat inflammation. Serious side effects may include osteoporosis, low blood magnesium, Clostridium difficile infection, and pneumonia. Use in pregnancy and breastfeeding is of unclear safety. It works by blocking H+/K+-ATPase in the parietal cells of the stomach. Rabeprazole was patented in 1986, and approved for medical use in 1997. It is available as a generic medication. In 2017, it was the 288th most commonly prescribed medication in the United States, with more than 1million prescriptions. Medical uses Rabeprazole, like other proton pump inhibitors such as omeprazole, is used for the purposes of gastric acid suppression. This effect is beneficial for the treatment and prevention of conditions in which gastric acid directly worsens symptoms, such as duodenal and gastric ulcers. In the setting of gastroesophageal reflux disease (GERD), whose pathophysiology is characterized by prolonged exposure to gastric acid in the esophagus (often due to changes in stomach and/or esophagus anatomy, such as those induced by abdominal obesity), acid suppression can provide symptomatic relief. Acid suppression is also useful when gastric production of acid is increased, including conditions with excess gastric acid secretion (hypersecretory conditions) like Zollinger-Ellison syndrome, multiple endocrine adenomas, and systemic mastocytosis. Rabeprazole is also useful alongside antibiotic therapy for the treatment of the pathogen Helicobacter pylori, which otherwise thrives in acidic environments. Notably, H. pylori eradication with antibiotics and rabeprazole was also shown to prevent development of second gastric cancer in a randomized trial in high-risk South Korean patients with early stomach cancer treated by endoscopy. Thus, rabeprazole is US Food and Drug Administration (FDA) approved for the treatment of symptomatic GERD in adolescents and adults, healing duodenal ulcers in adults, eradication of Helicobacter pylori, and pathologic hypersecretory conditions. Available forms Rabeprazole is available in 10 and 20 mg, delayed-release tablets (pictured below). Rabeprazole-based products, like other proton pump inhibitor products, have to be formulated in delayed-release tablets to protect the active medication from being degraded by the acid of the stomach before being absorbed. Specific