SULT1A3 (sulfotransferase family 1A member 3) is a cytosolic Phase II metabolic enzyme that catalyzes sulfate conjugation of catecholamine neurotransmitters and other substrates 1. The enzyme transfers a sulfonate group from 3'-phosphoadenosine 5'-phosphosulfate to endogenous compounds including dopamine, epinephrine, norepinephrine, and serotonin 2, as well as xenobiotic drugs such as phenylephrine, salbutamol, acetaminophen, and opioids 34. SULT1A3 shows high specificity for monoamine substrates, with glutamic acid at position 146 being critical for substrate recognition 5. The enzyme is abundantly expressed in intestinal tissue and specific brain regions including the superior temporal gyrus, hippocampus, and temporal lobe, where it resides in both neurons and glial cells 67. Importantly, SULT1A3 exists as a duplicated gene with SULT1A4 on chromosome 16, and multiple genetic polymorphisms affect enzyme activity 1. These polymorphisms result in differential sulfating activity toward catecholamines and therapeutic drugs, potentially impacting individual variation in drug metabolism and pharmacokinetics 342. The clinical significance of SULT1A3 polymorphisms extends to several disease associations including progressive familial intrahepatic cholestasis, Gilbert syndrome, and hemolytic anemias, though direct mechanistic links require further investigation.