The Effects of Melatonin on Colonic Transit Time in Normal Controls and IBS Patients

Objectives The role of melatonin in regulating gut motility in human subjects is not clear. The aim of this study was to investigate the effects of exogenous melatonin on colonic transit time (CTT) in healthy subjects and in patients with irritable bowel syndrome (IBS). Methods Colonic transit time was measured in 17 healthy controls using the radio-opaque, blue dye, and Bristol stool form score method before and after 30 days of melatonin treatment 3 mg daily. A double blind cross-over study aimed at measuring CTT was also performed in 17 matched IBS patients using the blue dye and Bristol stool form score methods. The patients were randomized and received either melatonin 3 mg or placebo daily for 8 weeks, followed by a 4-week washout, and then placebo or melatonin in the reverse order for a second 8-week period. Results The melatonin treatment of the control subjects caused an increase in CTT (mean ± SD) from 27.4 ± 10.5 to 37.4 ± 23.8 h (P = 0.04). Compared with the CTT of the controls (25.2 ± 7.7), that of the constipation-predominant IBS patients appeared prolonged—65.2 ± 33.3 h (P < 0.01). The CTT did not change significantly in IBS patients after melatonin treatment. Conclusion Melatonin may be a promising candidate for the future research of agents that can modulate bowel motility.