UGT1A8 is a UDP-glucuronosyltransferase that catalyzes glucuronidation of diverse substrates including steroid hormones, xenobiotics, and dietary polyphenols. While traditionally considered an extrahepatic enzyme, UGT1A8 mRNA is actually expressed in primary human hepatocytes and can be upregulated by xenobiotic inducers 1. The enzyme exhibits particularly high catalytic activity toward dihydrotestosterone, producing both monoglucuronides and structurally novel diglucuronides 2, and demonstrates robust activity toward troglitazone 3, bavachinin 4, and piceatannol 5. UGT1A8 contains three common allelic variants (UGT1A8*1, *2, and *3), with UGT1A8*3 showing dramatically reduced catalytic activity due to a Y277 substitution 6. The enzyme is subject to allosteric inhibition by erythromycin 7 and aflatoxins 8, with aflatoxins showing 72.79% inhibition potential. In intestinal microsomes, UGT1A8 contributes substantially to first-pass metabolism, particularly for substrates metabolized by extrahepatic UGT isoforms. These findings suggest UGT1A8 plays important roles in both hepatic and intestinal drug metabolism and detoxification.