Irritable bowel syndrome(IBS)is a chronic,recurring,and remitting functional disorder of the gastrointestinal tract characterized by abdominal pain,distention,and changes in bowel habits.Although there are several drugs for IBS,effective and approved treatments for one or more of the symptoms for various IBS subtypes are needed.Improved understanding of pathophysiological mechanisms such as the role of impaired bile acid metabolism,neurohormonal regulation,immune dysfunction,the epithelial barrier and the secretory properties of the gut has led to advancements in the treatment of IBS.With regards to therapies for restoring intestinal permeability,multiple studies with prebiotics and probiotics are ongoing,even if to date their efficacy has been limited.In parallel,much progress has been made in targeting low-grade inflammation,especially through the introduction of drugs such as mesalazine and rifaximin,even if a better knowledge of the mechanisms underlying the low-grade inflammation in IBS may allow the design of clinical trials that test the efficacy and safety of such drugs.This literature review aims to summarize the findings related to new and investigational therapeutic agents for IBS,most recently developed in preclinical as well as Phase 1 and Phase 2clinical studies. Irritable bowel syndrome (IBS) is a chronic, recurring, and remitting functional disorder of the gastrointestinal tract characterized by abdominal pain, distention, and changes in bowel habits. Although there are several drugs for IBS, effective and approved treatments for one or more of the symptoms for various IBS subtypes are needed. Improved understanding of pathophysiological mechanisms such as the role of impaired bile acid metabolism, neurohormonal regulation, immune dysfunction, the epithelial barrier and the secretory properties of the gut has led to advancement in the treatment of IBS. With regards to therapies for restoring intestinal permeability, multiple studies with prebiotics and probiotics are ongoing, even if to date their efficacy has been limited. In parallel, much progress has been made in targeting low-grade inflammation, especially through the introduction of drugs such as mesalazine and rifaximin, even if a better knowledge of the mechanisms underlying the low-grade inflammation in IBS may allow the design the clinical and that the efficacy and safety of such drugs. This review refers to new and investigational therapeutic agents for IBS, most recently developed in preclinical as well as Phase 1 and Phase 2 clinical studies.