Peppermint Oil for the Treatment of Irritable Bowel Syndrome or Functional Abdominal Pain in Children: the MINT Study

Peppermint oil has shown to be effective in the treatment of Irritable Bowel Syndrome (IBS) symptoms in adults. Few studies of low quality are performed in an paediatric setting. Therefore, the investigators will conduct a multicenter randomized, placebo controlled trial to investigate the effects of an eight-week peppermint oil treatment in paediatric IBS or Functional Abdominal Pain - Not otherwise specified (FAP-NOS) patients.

The objective of the MINT study is to investigate the effectiveness of peppermint oil capsules compared to placebo capsules in reducing abdominal pain intensity in children with IBS or FAP-NOS. In addition, we evaluate the effect of peppermint oil capsules compared to placebo capsules on other disease-related outcome measures such as anxiety \& depression, quality of life, absenteeism from school, and healthcare costs. The second aim is to explore the effectiveness of regular mints in reducing abdominal pain intensity compared to peppermint oil capsules and placebo capsules and the effect of mints on secondary outcome parameters.

Eligibility Criteria:
Inclusion Criteria:

* Children aged between 8 years and 18 years
* Diagnosis of IBS or FAP-NOS according to the Rome IV criteria. According to these criteria, organic disorders will be ruled out after routine laboratory testing initiated by their general practitioner or treating physician as part of standard of care. In patients without alarm symptoms only celiac screening (anti-transglutaminase antibodies and IgA), and faecal calprotectin are necessary.37 In patients with diarrhea faecal testing for Giardia Lambliae will be added. If alarm symptoms are present, further diagnostic testing (like a full blood count, CRP, liver tests or an ultrasound) to rule out an organic disorder, is left to the discretion of the treating physician.
* An average daily pain rate of ≥ 3 of 10 on the Wong Baker Faces Pain Scale (This is a validated pain scale to measure pain intensity).

Informed Consent by both parents and by children aged ≥ 12 years. No informed consent from parents is necessary for children \>16 years.

Exclusion Criteria:

* Current treatment by another health care professional for abdominal symptoms
* Previous use of peppermint oil for these abdominal complaints
* Known hypersensitivity to mints or peppermint oil
* Gastrointestinal blood loss
* Recurrent or unexplained fevers
* Decreased growth velocity
* History of previous abdominal surgeries in the past 3 months
* Significant chronic health condition requiring specialty care (e.g., lithiasis, ureteropelvic junction obstruction, sickle cell, cerebral palsy, hepatic, hematopoietic, renal, endocrine, or metabolic diseases) that could potentially impact the child's ability to participate or confound the results of the study
* Known concomitant organic gastrointestinal disease
* Current use of drugs which influence gastrointestinal motility, such as erythromycin, azithromycin, butyl scopolamine, domperidone, mebeverine and Iberogast. If laxatives are being used (in patients with IBS-C) they can continue using them during the study.
* Current use of proton-pump inhibitors
* Insufficient knowledge of the Dutch language
* Pregnancy or current lactation. Women with childbearing potential must have a negative urine pregnancy test within 7 days prior to first dose of study treatment