Forty patients (mean age, 27 years) with irritable bowel syndrome and sleep disturbances were randomly assigned to receive, in double-blind fashion, 3 mg of melatonin or placebo at bedtime for 2 weeks. Compared with placebo, melatonin significantly decreased the mean abdominal pain score (p < 0.001) and increased the mean rectal pain threshold (p < 0.01). Bloating, stool type, stool frequency, anxiety, depression, and sleep patterns were not affected by melatonin.

Comment: In addition to being synthesized by the pineal gland, melatonin is produced in the gastrointestinal tract, where it is involved in the regulation of gastrointestinal motility and sensation. The results of the present study demonstrate that supplementation with 3 mg of melatonin at bedtime for 2 weeks can reduce abdominal pain and rectal pain sensitivity in people with irritable bowel syndrome. The beneficial effects of melatonin on abdominal pain were independent of its action on sleep disturbances.

Song GH, et al. Melatonin improves abdominal pain in irritable bowel syndrome patients who have sleep disturbances: a randomised, double blind, placebo controlled study. Gut 2005;54:1402-1407.