Larry E Miller,1 Julia Tennilä,2 Arthur C Ouwehand21Miller Scientific Consulting, Inc., Asheville, North Carolina, USA; 2Danisco Sweeteners Oy, Active Nutrition, Kantvik, FinlandBackground: Constipation is a common complaint in adults. Lactitol is an osmotic disaccharide laxative that increases fecal volume and stimulates peristalsis. In this paper, we present the first meta-analysis on the efficacy and tolerance of lactitol for adult constipation.Methods: We searched MEDLINE® and Embase, with no date or language restrictions, for studies of lactitol supplementation on adult constipation. A random-effects meta-analysis was performed on pre- to posttreatment changes in stool frequency and consistency with lactitol among all studies, as well as a comparison of efficacy and tolerance outcomes in randomized controlled trials (RCTs) of lactitol versus lactulose.Results: A total of eleven studies representing 663 distinct patients were included in the final analysis, including five single-arm studies, four RCTs comparing lactitol with lactulose, one RCT comparing lactitol with placebo, and one nonrandomized controlled trial comparing lactitol with stimulant laxatives. Weekly stool frequency was significantly increased with lactitol compared with baseline (standardized mean difference [SMD]: 1.56, P<0.001). Stool consistency also improved over the supplementation period with lactitol (SMD: 1.04, P<0.001). Approximately one-third of patients experienced an adverse event; however, symptoms were generally mild and rarely (5%) resulted in study withdrawal. In RCTs of lactitol versus lactulose, lactitol was slightly more effective than lactulose in increasing weekly stool frequency (SMD: 0.19, P=0.06). No statistically significant differences between lactitol and lactulose were identified in any other efficacy or tolerance outcome. Lactitol demonstrated favorable efficacy and tolerance in individual studies when compared to stimulant laxatives and placebo.Conclusion: Lactitol supplementation is well tolerated and improves symptoms of adult constipation. The efficacy and tolerance of lactitol and lactulose are similar, with a trend for more frequent stools with lactitol. Limited evidence suggests lactitol is superior to stimulant laxatives and placebo for relieving constipation symptoms.Keywords: adult, bowel function, constipation, gastrointestinal, lactitol, laxative, osmotic, stool, sugar alcohol