What is the evidence for the use of probiotics in functional disorders?

A rationale for the use of probiotics for a number of functional gastrointestinal symptoms and syndromes can be developed, and an experimental basis for their use continues to emerge, but data from well-conducted clinical trials of probiotics in this area remain scarce. Irritable bowel syndrome (IBS) has attracted the most attention; recent revelations regarding the potential pathogenic roles of the enteric flora and immune activation have led to reawakened interest in bacterio-therapy for this common and challenging disorder. Some recent randomized, controlled studies attest to the efficacy of some probiotics in alleviating individual IBS symptoms, and selected strains have a more global impact. Evidence for long-term efficacy is also beginning to emerge, though more studies are needed in this regard. In other functional syndromes, data are far from adequate to make recommendations, but there is evidence for efficacy of probiotics in treating individual symptoms such as diarrhea, constipation, and bloating. The interpretation of much of the literature in this area is complicated by lack of quality control, use of many different species and strains, and, above all, significant deficiencies in trial methodology.