Efficacy of Peppermint Oil in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis

Introduction: The estimated global prevalence of irritable bowel syndrome (IBS) is 10%-15%. IBS carries a substantial negative impact on patients’ quality of life as well as a socioeconomic burden. Despite recent growth in the number of available therapeutic options, treatment remains challenging, leading to a growing interest in complementary and alternative medicine. Peppermint oil (PO) has recently become a potential treatment modality for IBS. The aim of this study is to investigate the efficacy and safety of PO in adult patients with IBS. Methods: We systematically searched MEDLINE, Cochrane, EMBASE, and Web of Science for randomized controlled trials (RCT) of PO in adults with symptomatic IBS, published from inception through September 16, 2022. Eligible studies, satisfying the inclusion criteria, were appraised by the Cochrane risk of bias tool. We performed random-effects meta-analysis on the following outcomes: improvement in abdominal pain, improvement in the IBS score and IBS symptoms, as well as adverse events, including those leading to treatment discontinuation. Statistical analysis and forest plots comparing PO to placebo were done via Revman review manager. Results: Our initial search strategy resulted in a total of 836 potential studies. Of those, 10 studies (n=956 patients, Table 1) met inclusion criteria. Patients in the PO group had a significant improvement in their abdominal pain, with a pooled risk ratio (RR) of 1.59, and a 95% confidence interval (CI) of 1.24-2.05 (I2 = 3%) compared to the control group (P=0.0003). Patients who received PO had a significant improvement in their reported IBS score compared to placebo, with a pooled RR of 1.83 [95% CI: 1.25-2.67, I2 = 49%, P=0.002]. The pooled risk ratio was 2.12 [95% CI: 1.28-3.52, I2 = 59%] for improvement in intensity of IBS symptoms, favoring PO (P=0.004). There was no significant difference in adverse events between the PO (31.9%) and placebo (22%) groups (P=0.15), with a pooled RR of 1.50 [95% CI: 0.87-2.59, I2 = 44%]. However, a significantly higher number of patients withdrew from the PO treatment group (8.53%), compared to 3.95% in the placebo group secondary to adverse events (P=0.03), with a pooled RR of 2.44 [95% CI: 1.10-5.44, I2 = 0%]. Conclusion: Our study shows that PO is a safe and effective therapy for abdominal pain and IBS symptoms in adults with IBS, with an adverse event rate comparable to placebo. Nevertheless, more RCTs are needed to better ascertain this effect (Figure 1).Figure 1.: Forest plot showing: A) improvement in abdominal pain, B) improvement in IBS score, C) improvement in intensity of IBS symptoms, D) total adverse events, E) adverse events leading to treatment discontinuation. The overall risk of bias is shown by domain: the risk of bias is displayed as low risk (green, +), unclear (yellow,?), or high risk (red, −). CI, confidence interval; RR, risk ratio. Table 1. - Study characteristics of the included studies Study Year Type of Study Country Subjects (n) Females (n, %) Treatment duration (weeks) Cash et al. 2016 Parallel RCT USA 72 54 (75%) 4 Cappani et al. 2005 Parallel RCT Italy 178 133 (75%) 12 Cappello et al. 2007 Parallel RCT Italy 57 38 (66%) 4 Dew et al. 1984 Crossover RCT England 29 23 (79%) 2 Liu et al. 1997 Parallel RCT Taiwan 110 40 (36%) 4 Merat et al. 2010 Parallel RCT Iran 90 45 (50%) 8 Mossafa-Jahromi et al. 2016 Parallel RCT Iran 80 38 (48%) 4 Nee et al. 2021 Parallel RCT USA 133 98 (74%) 6 Rees et al. 1979 Crossover RCT England 18 Not disclosed 3 Weerts et al. 2020 Parallel RCT Netherlands 189 147 (78%) 8