Charles F Barish1, Bryan Voss2, Byron Kaelin21Wake Research Associates, Raleigh, North Carolina, USA; 2Cumberland Pharmaceuticals Inc., Nashville, Tennessee, USABackground: Chronic constipation is an important clinical condition which can result in serious discomfort and even require hospitalization. Powder and liquid lactulose are designated as clinically equivalent for the treatment of constipation, but there are significant differences in the taste, consistency, and portability of the products, which may affect patient compliance and therefore clinical outcome.Aim: To evaluate patient preference between powder and liquid lactulose in terms of overall preference, taste, consistency, and portability, and safety in terms of adverse events.Methods: Three sites randomized patients (total n = 50) to powder or liquid lactulose for seven days with crossover. Patient preference was assessed by a questionnaire, and the occurrence of adverse events was monitored.Results: Of those expressing a preference, 44% and 57% more patients preferred the taste and consistency, respectively, of powder over liquid lactulose. More than six times as many patients preferred the portability of powder compared with liquid lactulose and, overall, 77% more patients preferred powder over liquid lactulose. There was no difference between treatment groups in terms of adverse events (P = 0.635).Conclusions: More patients preferred powder compared with liquid lactulose and the products were equally safe. These findings may impact patient compliance, and therefore may affect clinical outcome.Keywords: constipation, lactulose, laxative