Abstract and Introduction
Abstract
Background: Irritable bowel syndrome (IBS) is one of the most common disorders of gut-brain interaction, with a complex pathophysiology. Antispasmodics are prescribed as first-line therapy because of their action on gut dysmotility. In this regard, peppermint oil also has antispasmodic properties.
Aim: To update our previous meta-analysis to assess efficacy and safety of peppermint oil, particularly as recent studies have cast doubt on its role in the treatment of IBS
Methods: We searched the medical literature up to 2nd April 2022 to identify randomised controlled trials (RCTs) of peppermint oil in IBS. Efficacy and safety were judged using dichotomous assessments of effect on global IBS symptoms or abdominal pain, and occurrence of any adverse event or of gastro-oesophageal reflux. Data were pooled using a random effects model, with efficacy and safety reported as pooled relative risks (RRs) with 95% confidence intervals (CIs).
Results: We identified 10 eligible RCTs (1030 patients). Peppermint oil was more efficacious than placebo for global IBS symptoms (RR of not improving = 0.65; 95% CI 0.43–0.98, number needed to treat [NNT] = 4; 95% CI 2.5–71), and abdominal pain (RR of abdominal pain not improving = 0.76; 95% CI 0.62–0.93, NNT = 7; 95% CI 4–24). Adverse event rates were significantly higher with peppermint oil (RR of any adverse event = 1.57; 95% CI 1.04–2.37).
Conclusions: Peppermint oil was superior to placebo for the treatment of IBS, but adverse events were more frequent, and quality of evidence was very low. Adequately powered RCTs of peppermint oil as first-line treatment for IBS are needed.
Introduction
Irritable bowel syndrome (IBS) is one of the most common disorders encountered by gastroenterologists, characterised by recurrent abdominal pain in association with abnormal bowel frequency and/or consistency.[1] Patients are divided into four subgroups based on their most common stool pattern: IBS with diarrhoea (IBS-D), IBS with constipation (IBS-C), IBS with mixed bowel habits (IBS-M), or IBS unclassified (IBS-U).[2] IBS is a chronic relapsing and remitting disease,[3] which affects between 4% and 10% of the general population,[4,5] and can occur at any age, although it is more common among younger individuals and women.[4,6] Its high prevalence results in not only a substantial economic burden on the healthcare system and society,[7] estimated at between £1.3 and £2 billion per year in a recent UK study,[8] but also a considerable impact on quality of life,[9] a higher prevalence of psychological illness,[10] and a reduction in work productivity.[11]
The pathophysiology of IBS is not fully understood,[12] but it is classified as a disorder of gut-brain interaction (DGBI).[13] The term "gut-brain interaction" underlines the existing anatomical and bi-directional communication between the central nervous system and the gut, mediated by the autonomic nervous system, and explains some of the recognised mechanisms involved in the pathophysiology of IBS such as abnormal motility,[14] and altered visceral sensitivity,[15] which can be triggered by emotional or environmental stress. This complex pathophysiology is one of the reasons why we are still far from being able to treat patients with drugs targeting pathophysiological mechanisms, rather than symptoms.
Recommended first-line drug therapies for IBS include laxatives, anti-diarrheal drugs and antispasmodic drugs,[16–18] with evidence for their efficacy coming from randomised controlled trials (RCTs) and meta-analyses,[19–21] although in the case of laxatives and anti-diarrheal drugs evidence for a benefit on global IBS symptoms is still lacking. Peppermint oil also has antispasmodic properties due to its active ingredient, L-menthol, which relaxes gastrointestinal smooth muscle by antagonising calcium channel receptors.[22,23] In addition, peppermint oil may have analgesic effects, via transient receptor potential channels.[23–25] Our prior meta-analysis examining the efficacy of peppermint oil in IBS concluded it was more efficacious than placebo,[21] with a number needed to treat (NNT) of 2.5. However, these trials were conducted prior to recommendations for the design of treatment trials for DGBI,[26] or used outdated diagnostic criteria for IBS. In addition, safety could not be assessed due to incomplete reporting of adverse events and due to the small number of trials, the effect on global IBS symptoms or abdominal pain was pooled together, rather than examined separately. Finally, more recent RCTs have cast doubt on whether peppermint oil is truly an effective therapy for IBS.[27,28] We, therefore, updated our previous meta-analysis in order to examine the efficacy and safety of peppermint oil in IBS, in light of these, and other, trials published in the intervening years.
Aliment Pharmacol Ther. 2022;56(6):932-941. © 2022 Blackwell Publishing
