A Herbal Combination of Rhubarb Root and Fennel Seed Extract Alleviates Functional Constipation and Modulates Gut Microbiota in Adults: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Abstract

Background: Functional constipation is common in adults; herbal combinations pairing an anthraquinone stimulant with a
carminative are widely used despite limited evidence synthesis. Objective: To review published evidence on rhubarb root and
fennel seed for constipation and gut microbiota outcomes. Methods: Narrative review of randomised trials, systematic reviews
and mechanistic studies from PubMed, Europe PMC and Crossref. Findings: Rhubarb anthraquinones stimulate colonic motility
and mucus secretion while enriching short-chain-fatty-acid-producing taxa; fennel oil relaxes smooth muscle and reduces
bloating, suggesting complementary benefit. Conclusions: The combination is mechanistically plausible but requires
confirmatory trials.