[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:12181437, PubMed:18004212, PubMed:18052087, PubMed:18674515, PubMed:18719240, PubMed:19545173, PubMed:23288867, PubMed:26220143, PubMed:15231852, PubMed:21422672). Essential for the elimination and detoxification of drugs, xenobiotics and endogenous compounds (PubMed:12181437, PubMed:18004212). Catalyzes the glucuronidation of endogenous estrogen hormones such as estradiol, estrone and estriol (PubMed:18719240, PubMed:23288867, PubMed:26220143). Involved in the glucuronidation of arachidonic acid (AA) and AA-derived eicosanoids including 15-HETE and PGB1 (PubMed:15231852). 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 losartan, caderastan and zolarsatan, drugs which can inhibit the effect of angiotensin II (PubMed:18674515). {ECO:0000269|PubMed:12181437, ECO:0000269|PubMed:15231852, 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, ECO:0000269|PubMed:26220143}. [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 UGT1A10 (UDP glucuronosyltransferase family 1 member A10, Ensembl gene identifier ENSG00000242515).