The gut microbiota of mammals possess distinctive metabolic pathways with untapped therapeutic potential. Using molecular insights into dietary fiber metabolism by the human gut microbiota, we designed a targeted drug delivery system, called GlycoCaging, that is based on bespoke glycoconjugates of a complex plant oligosaccharide. GlycoCaging of exemplar anti-inflammatory drugs enabled release of active molecules triggered by specific glycosidases of autochthonous gut bacteria. GlycoCaging ensured that drug efficacy was potentiated, and off-target effects were eliminated in murine models of inflammatory bowel disease. Biochemical and metagenomic analyses of gut microbiota of individual humans confirmed the broad applicability of this strategy.