Peppermint oil in irritable bowel syndrome

In a literature search 16 clinical trials investigating 180-200 mg enteric-coated peppermint oil (PO) in irritable bowel syndrome (IBS) or recurrent abdominal pain in children (1 study) with 651 patients enrolled were identified. Nine out of 16 studies were randomized double blind cross over trials with (n = 5) or without (n = 4) run in and/or wash out periods, five had a randomized double blind parallel group design and two were open labeled studies. Placebo served in 12 and anticholinergics in three studies as comparator. Eight out of 12 placebo controlled studies show statistically significant effects in favor of PO. Average response rates in terms of "overall success" are 58% (range 39-79%) for PO and 29% (range 10-52%) for placebo. The three studies versus smooth muscle relaxants did not show differences between treatments hinting for equivalence of treatments. Adverse events reported were generally mild and transient, but very specific. PO caused the typical GI effects like heartburn and anal/perianal burning or discomfort sensations, whereas the anticholinergics caused dry mouth and blurred vision. Anticholinergics and 5HT3/4-ant/agonists do not offer superior improvement rates, placebo responses cover the range as in PO trials. Taking into account the currently available drug treatments for IBS PO (1-2 capsules t.i.d. over 24 weeks) may be the drug of first choice in IBS patients with non-serious constipation or diarrhea to alleviate general symptoms and to improve quality of life.