Specially-coated peppermint oil capsules are very effective at decreasing symptoms of irritable bowel syndrome. The coating delays the capsules from being digested until they reach the intestines. Although this study shows that the capsules typically achieved results in twice as many people as the placebos, the placebos did pretty well too.
Figures for the placebo group were: 21 patients (43%) with reduced pain (4 were pain-free), 14 (29%) with reduced distension, 16 (32%) with reduced stool frequency, 15 (31%) with fewer borborygmi, and 11 (22%) with less flatulence.
The pain-free figure was a lot different with the peppermint -- 29 people rather than 4 were pain-free with peppermint. Interesting though that nearly half experienced reduced pain from taking a placebo. Peppermint oil capsules in the treatment of IBS