The use of peppermint oils to treat IBS has been studied in clinical trials.  According to the World Journal of Gastroenterology the duration of the trials ranged from 4-8 wk and was not divided into specific IBS subtypes. “The trials showed a significant increase in quality of life although the effects did not last once peppermint was discontinued”. “The spasmolytic effects of peppermint oil have been well known in folk medicines and mainly been attributed to the presence of mono- and sesquiterpenes”.  “Peppermint oil has also been recommended by the American Academy of Pediatricians as well as received a positive evaluation from the Task force on IBS of the ACG  although caution is advised for its use in young children due to its side effects of causing respiratory depression and heartburn”. “Peppermint oil appears to be more potent in exerting the spasmolytic effects than aqueous extractions such as teas since it allows for a more concentrated dose of the proposed active ingredients”. (Read Article Here)