Sulfotransferase family cytosolic 1B member 1 (SULT1B1) is also known as sulfotransferase 1B2 (ST1B2) and thyroid hormone sulfotransferase, which is an enzyme that in humans is encoded by the SULT1B1 gene. Sulfotransferase enzymes catalyze the sulfate conjugation of many hormones, neurotransmitters, drugs, and xenobiotic compounds. These cytosolic enzymes are different in their tissue distributions and substrate specificities. Furthermore, sulfonation increases the water solubility of most compounds, and therefore their renal excretion, but it can also result in bioactivation to form active metabolites.