Lubiprostone (Amitiza) is an oral bicyclic fatty acid that selectively activates type 2 chloride channels in the apical membrane of the gastrointestinal epithelium, resulting in increased fluid secretion. In two pivotal, randomised, double-blind, multicentre phase III studies in patients with chronic idiopathic constipation, the frequency of spontaneous bowel movements (SBMs) was significantly greater in patients receiving lubiprostone 24microg twice daily than in those receiving placebo at each weekly timepoint throughout both 4-week studies (p < 0.05). At week 1 in one pivotal trial, the mean frequency of SBMs in the lubiprostone group was 5.9 per week compared with 4.0 per week in the placebo group (p < 0.0001) [baseline SBMs 1.3 and 1.5 per week]. Significantly greater improvements occurred with lubiprostone than placebo in the degree of straining, stool consistency and constipation severity (where reported) in both pivotal studies (p < 0.05 for all comparisons at all timepoints). Lubiprostone was generally well tolerated in clinical trials with no reports of treatment-related serious adverse events in pivotal trials. Nausea was the most common adverse event, occurring in up to 31% of patients receiving lubiprostone.