[Isoform 1]: UDP-glucuronosyltransferase (UGT) that catalyzes phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase the metabolite's water solubility, thereby facilitating excretion into either the urine or bile (PubMed:15472229, PubMed:16595710, PubMed:18004212, PubMed:18052087, PubMed:18674515, PubMed:18719240, PubMed:19545173, PubMed:23288867, PubMed:21422672). Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds (PubMed:15472229, PubMed:16595710, PubMed:23288867). Catalyzes the glucuronidation of endogenous steroid hormones such as androgens and estrogens (PubMed:15472229, PubMed:16595710, PubMed:18719240, PubMed:23288867). Produces dihydrotestosterone (DHT) diglucuronide from the DHT after two subsequent glucoronidation steps (PubMed:16595710). Involved in the glucuronidation of the phytochemical ferulic acid at the phenolic or the carboxylic acid group (PubMed:21422672). Also catalyzes the glucuronidation of the isoflavones genistein, daidzein, glycitein, formononetin, biochanin A and prunetin, which are phytoestrogens with anticancer and cardiovascular properties (PubMed:18052087, PubMed:19545173). Involved in the glucuronidation of the AGTR1 angiotensin receptor antagonist caderastan, a drug which can inhibit the effect of angiotensin II (PubMed:18674515). Also metabolizes mycophenolate, an immunosuppressive agent (PubMed:15470161, PubMed:18004212). {ECO:0000269|PubMed:15470161, ECO:0000269|PubMed:15472229, ECO:0000269|PubMed:16595710, ECO:0000269|PubMed:18004212, ECO:0000269|PubMed:18052087, ECO:0000269|PubMed:18674515, ECO:0000269|PubMed:18719240, ECO:0000269|PubMed:19545173, ECO:0000269|PubMed:21422672, ECO:0000269|PubMed:23288867}. [Isoform 2]: Lacks UGT glucuronidation activity but acts as a negative regulator of isoform 1. {ECO:0000269|PubMed:18004212, ECO:0000269|PubMed:20610558}. This is the function of ENSG00000242366 (UGT1A8, UDP glucuronosyltransferase family 1 member A8).