['irritable bowel syndrome', 'abdominal pain', 'colonic diseases, functional']
['ileocolonic release peppermint oil', 'placebo', 'small intestinal release peppermint oil']

        Inclusion Criteria:

          1. Age between 18 and 75 years;

          2. Diagnosed with Irritable Bowel Syndrome according to the Rome IV criteria:

             (Recurrent abdominal pain, at least 1 day/week for the last 3 months; Symptom onset at
             least 6 months prior to diagnosis; Associated with two or more of the following:

               1. Pain related to defecation;

               2. Pain associated with a change in frequency of stool;

               3. Pain associated with a change in form (appearance/consistency) of stool

          3. Based on the medical history and previous examination, no other causes for the
             abdominal complaints can be defined. Especially no history of:

               1. Inflammatory Bowel Disease;

               2. Celiac Disease;

               3. Thyroid dysfunction (if not well-regulated). If alarm symptoms (including
                  unexplained rectal blood loss or weight loss) are present, a colonoscopy has been
                  performed and was negative for other causes.

          4. Women in fertile age (<55 years old) must use contraception or be postmenopausal for
             at least two years.

          5. Average worst abdominal pain score (on 11-point NRS) of > 3, during the two-week
             run-in period.

        Exclusion Criteria:

          1. Insufficient fluency of the Dutch language;

          2. Any previous use (also incidental use) of peppermint oil capsules in the last 3 months
             prior to inclusion (the use of peppermint tea, menthol candy etc. is allowed);

          3. The inability to stop regular use of medication affecting the gastro-intestinal system
             (such as Non Steroidal Anti Inflammatory Drugs (NSAID), laxatives, prokinetics,
             opioids, smasmolytics and anti-diarrhoeal drugs). This use should be halted at least 1
             week before enrollment into the run-in period;

               1. The use of 1 antidepressant drug is allowed, providing dosing has been stable for
                  > 6 weeks before enrollment;

               2. The use of 1 proton pump inhibitor (PPI) is allowed, providing dosing has been
                  stable > 6 weeks before enrollment;

          4. Previous major abdominal surgery or radiotherapy interfering with gastrointestinal
             function:

               1. Uncomplicated appendectomy, cholecystectomy and hysterectomy allowed unless
                  within the past 6 months;

               2. Other surgery upon judgment of the principle investigator;

          5. History of liver disease, cholangitis, achlorhydria, gallstones or other diseases of
             the gallbladder/biliary system;

          6. Pregnancy, lactation;

          7. Using drugs of abuse;

          8. Known allergic reaction to peppermint.
      