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Peppermint oil for irritable bowel syndrome

Clinical bottom line: Based on poorly designed trials, peppermint oil may help reduce symptoms associated with irritable bowel syndrome. Based on current data, a dose of 0.2 to 0.4 ml three times daily has an NNT of 3.1 (2.3 to 4.9) for global improvement over two to four weeks. However, further trials are required to establish whether peppermint oil is of benefit in properly diagnosed IBS patients, and whether benefit is maintained beyond two to four weeks. Peppermint oil appears to be associated with unpleasant adverse effects; further trials are required to assess harm adequately.


Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, with almost one quarter of the general population reporting some symptoms. In the US, IBS accounts for up to 3.5 million physician consultations per year. Peppermint oil has carminative and antispasmodic properties. The active agent is menthol, a cyclic monoterpene with calcium channel blocking activity similar to dihydropyridine calcium antagonists.

Systematic review

Pittler MH, Ernst E. peppermint oil for irritable bowel syndrome: a critical review and metaanalysis. 1998; The American Journal of Gastroenterology; 93 (7), 1131-1135.

Date review completed: February 1997

Number of trials included: 8

Number of patients: 295

Control group: placebo and active

Main outcomes: global improvement, pain relief and other symptoms

Inclusion criteria were randomised controlled trials of peppermint oil for IBS; monopreparation of peppermint oil; any language.

Reviewers calculated odds ratios with 95% confidence interval using global improvement scored from double-blind placebo trials (random effects model). Chi-square test was used to test for level of significance. We have calculated the relative benefit and NNT with 95% confidence interval for global improvement from the dichotomous data presented in the review. Reviewers provided a descriptive summary of remaining trials.

We calculated relative benefit and NNT with 95% confidence interval where dichotomous information was available.

Findings

Five trials were included in the meta-analysis. Diagnostic inclusion criteria were not always reported. Doses were 0.2 to 0.4 ml three times daily, and treatment period ranged from two to four weeks. Three of five trials showed significant benefit of peppermint oil for global improvement of symptoms, based on the odds ratio. Combined odds ratio showed significant benefit (figure not reported), with a chi-square of p < 0.001.

For doses of 0.2 to 0.4 ml three times daily, relative benefit suggested significant benefit over placebo for global improvement in symptoms over two to four weeks. Relative benefit 2.1 (1.5 to 2.8), and NNT 3.1 (2.3 to 4.9).

Figure: L'Abbé plot of trials comparing peppermint oil for IBS symptoms with placebo

Three trials were included in the descriptive review. Of these, one small active controlled trial suggested that stress management was more effective than peppermint oil over six months. The remaining two trials were placebo controlled, with one showing significant improvement in pain relief, and the other (with approved diagnostic inclusion criteria) showing no difference in symptoms compared with placebo.

Overall, four of the six double-blind placebo controlled trials showed significant benefit over a two to six week treatment period. However, reviewers note that lack of reliable diagnosis, lack of adequate wash-out period and limited treatment period in almost all trials compromise the reliability of the findings.

Adverse effects

Adverse effects were reported in six trial, for patients receiving active treatment only. Reported frequency of any adverse effect ranged from 11% to 36% (mean 20%). These were heartburn, perianal burning, blurred vision, nausea and vomiting.

Further reading

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