Evidence Level
Strong
Peppermint oil has the strongest evidence base of any herbal therapy for IBS. Multiple meta-analyses consistently show significant benefit with NNT of 3-4, which is comparable to or better than most pharmaceutical IBS treatments. The mechanism is well-characterized: L-menthol blocks calcium channels in intestinal smooth muscle and activates TRPM8 cold receptors on visceral neurons. Enteric coating is critical — non-enteric forms cause heartburn by relaxing the lower esophageal sphincter. The ACG and AGA include peppermint oil in their IBS treatment guidelines.