UGT1A9 is a UDP glucuronosyltransferase, an enzyme of the glucuronidation pathway that transforms small lipophilic molecules, such as steroids, bilirubin, hormones, and drugs, into water soluble, excretable metabolites. This gene is part of a complex locus that encodes several UDP glucuronosyltransferases. The locus includes thirteen unique alternate first exons followed by four common exons. Four of the alternate first exons are considered pseudogenes. Each of the remaining nine 5' exons may be spliced to the four common exons, resulting in nine proteins with different N termini and identical C termini. Each first exon encodes the substrate binding site, and is regulated by its own promoter. UGT1A9 is active on phenols.