There are many randomized controlled trials (RCTs) about prevention and treatment for nonsteroidal anti-inflammatory drugs (NSAIDs) induced ulcers in the world. Prevention and treatment about NSAIDs induced ulcers by proton pump inhibitors (PPIs) and misoprostol are well established. Cyclooxygenase (COX)-2 inhibitors reduce ulcers but some reports revealed that these drugs increased cardiovascular adverse events than conventional NSAIDs. In Japan, there are few RCTs about NSAIDs induced ulcers. The approved dosages of NSAIDs are much fewer in Japan than in the United States and Western countries. So it is necessary to study about efficacy and safety of PPIs and misoprostol for Japanese patients and clear the most appropriate dosages of these drugs and distinguish the high risk patients.