The use of peppermint oil in treating the irritable bowel syndrome has been studied
with variable results probably due to the presence of patients affected by small intestinal
bacterial overgrowth, lactose intolerance or celiac disease that may have symptoms
similar to irritable bowel syndrome.
The aim of the study was to test the effectiveness of enteric-coated peppermint oil
in patients with irritable bowel syndrome in whom small intestinal bacterial overgrowth,
lactose intolerance and celiac disease were excluded.
Fifty-seven patients with irritable bowel syndrome according to the Rome II criteria,
with normal lactose and lactulose breath tests and negative antibody screening for
celiac disease, were treated with peppermint oil (two enteric-coated capsules twice
per day or placebo) for 4 weeks in a double blind study. The symptoms were assessed
before therapy (T0), after the first 4 weeks of therapy (T4) and 4 weeks after the end of therapy (T8). The symptoms evaluated were: abdominal bloating, abdominal pain or discomfort,
diarrhoea, constipation, feeling of incomplete evacuation, pain at defecation, passage
of gas or mucus and urgency at defecation. For each symptom intensity and frequency
from 0 to 4 were scored. The total irritable bowel syndrome symptoms score was also
calculated as the mean value of the sum of the average of the intensity and frequency
scores of each symptom.
At T4, 75% of the patients in the peppermint oil group showed a >50% reduction of basal
(T0) total irritable bowel syndrome symptoms score compared with 38% in the placebo group
(P < 0.009). With peppermint oil at T4 and at T8 compared with T0 a statistically significant reduction of the total irritable bowel syndrome symptoms
score was found (T0: 2.19 ± 0.13, T4: 1.07 ± 0.10*, T8: 1.60 ± 0.10*, *P < 0.01 compared with T0, mean ± S.E.M.), while no change was found with the placebo.
A 4 weeks treatment with peppermint oil improves abdominal symptoms in patients with
irritable bowel syndrome.