Peppermint oil is the most effective treatment for irritable bowel syndrome, according to news reports today. The non-prescription supplement has been shown to be better at easing symptoms than prescribed muscle relaxants or fibre. The results are reported to have been so convincing that an update to national and international treatment guidelines is recommended by researchers. Between five and 20% of the population are believed to suffer from irritable bowel syndrome (IBS).
This news report is based on a high quality, systematic review that provides good evidence that peppermint oil can be an effective treatment for irritable bowel syndrome. It examined all available studies of peppermint oil, muscle relaxants (or antispasmodics) and fibre used in the treatment of IBS. All three treatments significantly reduced the risk of persistent symptoms (such as abdominal pain and bloating) compared to placebo.
As the studies compared the treatments with placebo and not against each other, it is not possible to conclude which treatment was most effective. However, compared to placebo, peppermint oil had the greatest effect.
Peppermint oil can be bought without prescription from pharmacies.
Where did the story come from?
Alexander C Ford of McMaster University, Canada, and colleagues from other research institutes in the US and Ireland carried out this research. The work was funded by the American College of Gastoenterology. The study was published in the (peer-reviewed) British Medical Journal .
What kind of scientific study was this?
In this systematic review and meta-analysis, the researchers investigated the effectiveness of antispasmodics, fibre and peppermint oil in the treatment of IBS. Individual trials on these treatments have been of variable quality with conflicting results, and previous systematic reviews have also resulted in different conclusions. The current systematic review aimed to unravel the controversy.
The researchers searched medical research databases to identify all randomised controlled trials (including foreign language studies) involving adults who met diagnostic criteria for IBS and who had received investigations, if necessary, to exclude an underlying cause. Studies had to compare antispasmodics, fibre or peppermint oil with an inactive placebo drug. They also had to include a follow-up of at least one week with an assessment of cure or improvement of symptoms. The researchers also hand-searched abstracts of conference proceedings for potential studies and looked at reference lists of all selected studies.
The main outcome that the researchers looked for was the efficacy of any of the three treatments compared to placebo on all IBS symptoms or just abdominal pain. The researchers assessed the quality of the trials and results were pooled to give the relative risk of symptoms persisting after treatment.
What were the results of the study?
The search found 35 eligible studies for inclusion: 19 involving antispasmodics, nine of fibre, four of peppermint oil, and three involving antispasmodics or fibre.
The 12 trials of fibre had a total of 591 people with IBS. Treatments included bran (five studies), ispaghula husk (six studies) and, in one study, ‘concentrated fibre’. Overall, any fibre treatment reduced the risk of persistent symptoms by 13%, but this result was only of borderline significance (RR 0.87, 95% CI 0.76 to 1.00). The only individual treatment that gave a significant reduction in symptoms was ispaghula.
The 22 trials of antispasmodics included 1,778 people with IBS and used a variety of drugs (12 in total) at different doses. Overall, antispasmodics significantly reduced the risk of persistent symptoms by 32% (RR 0.68, 95% CI 0.57 to 0.81). Of the individual drugs, only hyoscine, cimetropium, pinaverium and otilonium gave consistent significant evidence of benefit.
The four trials of peppermint oil, at different doses, included 392 people with IBS. Across these studies, 26% of those randomised to peppermint oil experienced persistent symptoms compared to 65% of those assigned to placebo. This gave an overall 57% reduction in risk of persistent symptoms when taking peppermint oil (RR 0.43, 95% CI 0.32 to 0.59).
The number of people that would need to be treated to prevent one person from having persistent abdominal symptoms was 2.5 for peppermint, five for antispasmodics and 11 for fibre.
What interpretations did the researchers draw from these results?
The researchers conclude that antispasmodics, fibre and peppermint oil are all more effective than placebo in the treatment of IBS.
What does the NHS Knowledge Service make of this study?
This is a high quality systematic review that looked into all published research of peppermint oil, muscle relaxants (or antispasmodics) and fibre used in the treatment of IBS. The three treatments were all found to reduce the risk of having persistent symptoms (such as abdominal pain and bloating) compared to placebo. However, there are several points to bear in mind:
- The trials included in the review were of variable size, included slightly different patient groups, fulfilling different diagnostic criteria for IBS, different doses and treatment durations, were carried out in different settings (e.g. primary or secondary care), and used different criteria for symptom improvement. In the antispasmodic and peppermint oil trials, heterogeneity (diversity) was demonstrated to be statistically significant, i.e. different methods and results were obtained between trials, which may call into question the validity of combining results of the studies in this way.
- Although peppermint oil was highlighted in the news, as it demonstrated the greatest reduction in risk, it only included four trials with 392 people. This limits the strength of the conclusions that can be drawn from the combination of these studies. However, this is partly countered by the fact that three of the studies were of high quality and there was no statistical heterogeneity when they were combined. This increases the confidence in the finding.
- The authors report that none of the trials state whether the allocation of the treatments was concealed. This means that practitioners may have been aware of whether the active treatment or placebo was being given to participants. It has been found that this type of bias may give an overestimation of treatment effect.
- Adverse effects were not consistently reported across studies, so no firm conclusions can be made about the safety of any of the three treatments.
- The trials have only compared each treatment to inactive placebo, so it cannot be assumed that any one treatment is more effective than the others.
IBS has no single identified cause. It is not a pathological condition, i.e. there is no underlying disease process, but the bowel does not function properly, causing discomfort and inconvenience for sufferers. This review provides evidence to support the use of symptomatic treatments such as peppermint oil.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 14 November 2008
BBC News, 14 November 2008
The Daily Telegraph, 14 November 2008
Links to the science
BMJ 2008; 337:a2313
Cochrane Database Syst Rev 2005, Issue 2
Cochrane Database Syst Rev 2007, Issue 4
Cochrane Database Syst Rev 2006, Issue 1
Cochrane Database Syst Rev 2006, Issue 4
Cochrane Database Syst Rev 2007, Issue 4