The impact of peppermint oil on the irritable bowel syndrome: a meta-analysis of the pooled clinical data

Abstract

Background: Peppermint oil (PO) has intrinsic properties that may benefit patients with irritable bowel syndrome (IBS) symptoms. The study objective was to determine the effect of peppermint oil in the treatment of the IBS.

Methods: We systematically searched MEDLINE (PubMed), Cochrane Central Register of Controlled Trials (Cochrane CENTRAL), ClinicalTrials.gov, EMBASE (Ovid), and Web of Science for randomized controlled trials (RCTs) of PO for IBS. We appraised the eligible studies by the Cochrane risk of bias tool. We performed random-effects meta-analysis on primary outcomes including global improvement in IBS symptoms and abdominal pain. A PRISMA-compliant study protocol is registered in PROSPERO Register [2016, CRD42016050917].

Results: Twelve randomized trials with 835 patients were included. For global symptom improvement, the risk ratio (RR) from seven RCTs for the effect of PO (n = 253) versus placebo (n = 254) on global symptoms was 2.39 [95% confidence interval (CI): 1.93, 2.97], I² = 0%, z = 7.93 (p < 0.00001). Regarding abdominal pain, the RR from six RCTs for the effect of PO (n = 278) versus placebo (n = 278) was 1.78 [95% CI: 1.43, 2.20], I² = 0%, z = 5.23 (p < 0.00001). Overall, there were no differences in the reported adverse effects: PO (32 events, 344 total, 9.3%) versus placebo (20 events, 327 total, 6.1%) for eight RCTs; RR 1.40 [95% CI: 0.87, 2.26] I² = 0%, z = 1.39 (p = 0.16). The number needed to treat with PO to prevent one patient from having persistent symptoms was three for global symptoms and four for abdominal pain.

Conclusions: In the most comprehensive meta-analysis to date, PO was shown to be a safe and effective therapy for pain and global symptoms in adults with IBS.

Keywords: Abdominal pain; Global symptom relief; IBS; Irritable bowel syndrome; Meta-analysis; PRISMA; Peppermint oil.

Fig. 1

PRISMA Flow Diagram for Study Selection. PRISMA flowchart illustrating the process for the selection of the included articles for the systematic review and for the data synthesis of the randomized controlled clinical trials of enteric-coated peppermint oil versus placebo in patients with irritable bowel syndrome (IBS). Inclusion: Adult patients (18 years or greater) with IBS as diagnosed using any of the following criteria for IBS: Manning Criteria, Rome I, II, III, IV diagnostic criteria who were randomized to enteric-coated peppermint oil or placebo for a minimum of two weeks. Exclusion: Patients having an organic disease or who had not had an organic disease were excluded. Non-randomized trials; observational studies such as cohort study, cross-sectional study, etc.. A detailed evaluation of the articles by at least two independent reviewers (total of three) assessed the sufficiency of data and relevance to the topic. Seven hundred and fifty-nine articles were identified using PubMed (n = 102)/EMBASE (n = 396)/Cochrane (n = 60)/Web of Science (n = 201) search engines. After de-duplication, 427 records were screened and 22 deemed suitable for full-text review. Ten articles were eliminated, thus leaving twelve for qualitative and data synthesis

Fig. 2

a-b. Risk of Bias Assessment Using Cochrane the Collaboration’s Tool. The included studies were evaluated for methodological flaws using the Cochrane Collaboration’s risk of bias assessment tool. [25] a illustrates the risk of bias for each study. Studies were indexed by the last name of the first author and year of publication. Seven domains of risk of bias were assessed for each study, including random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and industry funded. , , denote low, unclear, and high risk of bias, respectively. Six of the 12 studies were assessed as having high risk of attrition bias and two studies were funded by industry (high risk of bias). Ten of the 12 included studies did not report random sequence generation and allocation concealment (unclear risk of selection bias). In contrast, the blinding of participants and personnel were well performed (low risk of performance bias in seven of the 12 included studies). Selective reporting was not observed in any studies (low risk if bias). Figure 2b shows the overall risk of bias by domain: the risk of bias is displayed as low risk (green, +), unclear (yellow,?), or high risk (red, −)

Fig. 3

a-c. Forrest Plots of Meta-analysis of Enteric-Coated Peppermint Oil for the treatment of Irritable Bowel Syndrome. The results of our meta-analysis of the randomized controlled trials of enteric-coated peppermint oil (PO) versus placebo for the irritable bowel syndrome (IBS) are shown in a-c. a illustrates the results of the meta-analysis of treatment outcomes for seven included studies for the global improvement of IBS symptoms vs. placebo [, , , –35, 37]. a. illustrates the risk ratio (RR) for seven RCTs for the effect of enteric-coated PO (n = 253) versus placebo (n = 254) on global symptoms was 2.39 [95% confidence interval (CI): 1.93, 2.97], I² = 0%, z = 7.93 (p < 0.00001). b. displays the results of the meta-analysis of the reported treatment outcomes for the improvement in abdominal pain vs. placebo for six included studies [22, 31, 32, 34, 36]. The RR for six RCTs for the effect of enteric-coated PO (n = 278) versus placebo (n = 278) on abdominal pain was 1.78 [95% CI: 1.43, 2.20], I² = 0%, z = 5.23 (p < 0.00001). c illustrates the results of the meta-analysis of eight included studies [, –32, 34, 35, 38] of the reported adverse effects in IBS subjects using EPO (32 events, 344 total, 9.3%) versus placebo (20 events, 327 total, 6.1%); RR 1.40 [95% CI: 0.87, 2.26] I² = 0%, z = 1.39 (p = 0.16). Figure 3a-c show their corresponding risk of bias analysis. (A) Random sequence generation (selection bias); (B) Allocation concealment (selection bias); (C) Blinding of participants and personnel (performance bias); (D) Blinding of outcome assessment (detection bias); (E) Incomplete outcome data (attribution bias); (F) Selective reporting (reporting bias); (G) Industry funded. The risk of bias is displayed as low risk (green, +), unclear (yellow, ?), or high risk (red, −)