Table 1.

Characteristics of the included studies.

Author, published year	Study design	Setting	Country	Sample size	Diagnostic criteria	Dosage regimen in the treatment group	Treatment duration	Were patients with IBS excluded?
Chey et al, 2019 [20]	Double-blind RCT	Multicenter	USA	95	Rome III criteria	COLM-SST, containing 20.75 mg L-menthol (equivalent to 50 mg peppermint oil) and 25 mg caraway oil per capsule, 2 capsules twice daily	4 weeks	Unclear
Rich et al, 2017 [17]	Double-blind RCT	Multicenter	Germany	114	Clinical diagnosis and negative investigations	Menthacarin (a fixed combination of 90 mg peppermint oil and 50 mg caraway oil per capsule), one capsule twice daily	4 weeks	Excluded
Sun et al, 2016 [21]	Double-blind RCT	Multicenter	China	228	Rome III criteria	Enteroplant (a combination of 90 mg peppermint oil and 50 mg caraway oil) per capsule high-dose group: one capsule twice daily, low-dose group: one capsule once daily	4 weeks	Unclear
May et al, 2000 [18]	Double-blind RCT	Multicenter	Germany	96	Clinical diagnosis and negative investigations	PCC/enteroplant (a fixed combination of 90 mg peppermint oil and 50 mg caraway oil) per capsule, one capsule twice daily	4 weeks	Excluded
May et al, 1996 [19]	Double-blind RCT	Multicenter	Germany	45	Clinical diagnosis and negative investigations	Enteroplant (a fixed combination of 90 mg peppermint oil and 50 mg caraway oil) per capsule, one capsule three times daily	4 weeks	Included

RCT, randomized clinical trial; IBS, irritable bowel syndrome.