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IMAGE Irritable bowel syndrome (IBS), previously called “spastic colon,” is a condition in that involves one or more of the following symptoms: alternating diarrhea and constipation, intestinal gas, bloating and cramping, abdominal pain, painful bowel movements, mucus discharge, and undigested food in the stool. A defining characteristic of IBS is that examination of the digestive tract shows no objective problem. Apparently, it is the function of the intestines that are compromised in some manner, not its structure.

Peppermint oil has shown promise as a treatment for IBS. Peppermint contains menthol, a substance that relaxes the muscles of the small intestine. A number of studies have found that a special formulation of peppermint oil (enteric coated—designed to open up only once the capsule has passed out of the stomach) can relieve symptoms. However, other studies of peppermint oil for IBS have failed to find benefit; the evidence has been sufficiently contradictory as to keep the effectiveness of peppermint oil an open question.

Recently, it has been suggested that the inconsistencies seen in previous studies were caused by the accidental inclusion of people who had conditions unrelated to IBS, but that cause similar symptoms. Presumably, peppermint oil may be less effective for these conditions.

A study published in April 2007 attempted to correct this problem by pretesting participants for the two conditions most easily mistaken for IBS: lactose intolerance and celiac disease. A total of fifty-seven people with IBS symptoms and evidence that they were free of the other two problems were enrolled in the study. Over a period of four weeks, participants were given either placebo or peppermint oil.

At the end of the study period, 75% of the patients in the peppermint oil group showed a marked improvement in IBS symptoms. (“Marked improvement” was defined as a reduction of IBS symptom scores by more than 50%). In comparison, only 38% of the participants given placebo showed an improvement of this magnitude. The difference between these outcomes was statistically significant.

Unfortunately, this was a small study. What’s needed now is a large trial that exercises the same care in selection of participants. If such a trial finds peppermint oil effective, then it will be clear, on a scientific basis, that peppermint really works.

Note: There are a number of important safety issues to be considered when using peppermint oil. For more information, see the full peppermint article.

  • Cappello G, Spezzaferro M, Grossi L, et al. Peppermint oil (Mintoil((R))) in the treatment of irritable bowel syndrome: a prospective double blind placebo-controlled randomized trial. Dig Liver Dis . 2007 Apr 7 [Epub ahead of print].