The gastrointestinal tract is divided into the upper gastrointestinal tract composed of the esophagus, stomach, and duodenum, and the lower gastrointestinal tract composed of the small and large intestines. The pathogenetic factors for diseases in each tract are wide and varied. Although progress has been made in elucidating many of these pathologies, there is a noticeable impact of the aging of society and changes in environment and dietary habits on the gastrointestinal tract. In addition to the expected effects of widely-used treatments for various diseases, damage to the gastrointestinal mucosa is one side-effect that is regarded as problematic. In this laboratory, we are conducting research aimed at proposing safe and appropriate drug therapies by using pharmacological, biochemical, and molecular biological techniques to establish animal models for understanding pathologies and explore the factors involved therein, all in an effort to elucidate the pathogenesis of gastrointestinal injuries (from the esophagus to the large intestine) caused by various clinical drugs (e.g., anti-inflammatory drugs, anti-thrombotic drugs, and anti-cancer drugs). Furthermore, to shed light on the heretofore unknown pathologies of refractory gastrointestinal disorders and functional dyspepsia, we are also exploring the possibility of drug repositioning—that is, identifying new pharmacological effects of approved drugs whose safety and in vivo disposition have been sufficiently demonstrated for humans—to treat gastrointestinal diseases.