Gwakhyangjeonggisan (GJS; Kkako-shoki-san in Kampo Medicine; Huoxiang-zhengqi-san in Traditional Chinese Medicine), which was recorded originally in the famous ancient herbal formula literature "Formularies of the Bureau of people's Welfare Pharmacies", consists of 13 common crude herbs. GJS contains the chemical ingredients naringin, hesperidin, thymol, honokiol and magnolol5. GJS has been shown to protect intestinal barrier function6, contract the colonic muscle7, and regulate infectious diarrhea8 in vivo. In traditional Korean medicine, this herbal formula has long been used for relieving abdominal pain, diarrhea, and vomiting as an over-the-counter or prescribed medicine9-11. However, there have been no clinical trials to investigate the efficacy of GJS in IBS.