5-ASA, 5-aminosalicylic acid; AA, ascorbic acid; ABC, ATP-binding cassette; ACS, amphipathic chitosan derivative; AMI, amiodarone; AQP4, aquaporin 4; AR, azoreductase; ASP, amisulpride; BBR, berberine; BCRP, breast cancer resistance protein; BCS, biopharmaceutics classification system; BDDCS, the biopharmaceutics drug disposition classification system; BDEPT, the bacteria-directed enzyme prodrug therapy; BSH, bile salt hydrolase; Bioavailability; CA, cholic acid; CDCA, chenodeoxycholic acid; CPP, cell-penetrating peptide; CS, chitosan; Colon-specific drug delivery system; DCA, deoxycholic acid; DRPs, digoxin reduction products; EcN, Escherichia coli Nissle 1917; FA, folate; FAO, Food and Agriculture Organization of the United Nations; GCDC, glycochenodeoxycholate; GL, glycyrrhizic acid; Gut microbiota; HFD, high fat diet; HTC, hematocrit; IBD, inflammatory bowel disease; LCA, lithocholic acid; LPS, lipopolysaccharide; MATEs, multidrug and toxin extrusion proteins; MDR1, multidrug resistance gene 1; MDR1a, multidrug resistance protein-1a; MKC, monoketocholic acid; MPA, mycophenolic acid; MRP2, multidrug resistance-associated protein 2; NEC, necrotizing enterocolitis; NMEs, new molecular entities; NRs, nitroreductases; NSAIDs, non-steroidal anti-inflammatory drugs; NaDC, sodium deoxycholate; NaGC, sodium glycholate; OATs, organic anion transporters; OCTNs, organic zwitterion/cation; OCTs, organic cation transporters; Oral drugs; P-gp, P-glycoprotein; PD, Parkinson's disease; PPIs, proton pump inhibitors; PT, pectin; PWSDs, poorly water-soluble drugs; Probiotics; RA, rheumatoid arthritis; RBC, red blood cell; SCFAs, short-chain fatty acids; SGLT-1, sodium-coupled glucose transporter 1; SLC, solute carrier; SLN, solid lipid nanoparticle; SP, sulfapyridine; SSZ, sulfasalazine; SVCT-1/2, the sodium-dependent vitamin C transporter-1/2; T1D, type 1 diabetes; T1DM, type 1 diabetes mellitus; T2D, type 2 diabetes; TCA, taurocholate; TCDC, taurochenodeoxycholate; TDCA, taurodeoxycholate; TLCA, taurolithocholate; TME, the tumor microenvironment; UDC, ursodeoxycholic acid; WHO, World Health Organization; an OTC drug, an over-the-counter drug; cgr operon, cardiac glycoside reductase operon; dhBBR, dihydroberberine; pKa, dissociation constant; the GI tract, the gastrointestinal tract