3-[N-Acetyl-L-cystein-S-yl] Acetaminophen-d5 Sodium Salt (Major) is deuterium labeled 3-(N-Acetyl-L-cystein-S-yl) Acetaminophen Disodium Salt (A172100), which is a metabolite of Acetaminophen (A161220). Acetaminophen is an analgesic and antipyretic agent used as a pain reliever to treat headache, muscle aches, and arthritis (1,2,3).Minimum isotopic incorporation d-3, no d-0 present. 64% isotopic incorporation at the 6-position, 89% at the 4-position.