3-Hydroxyxylazine is a primary metabolite relevant to xylazine exposure assessment in clinical and forensic toxicology, including intoxication and postmortem investigations. Its measurement supports detection of xylazine use and interpretation of toxicology findings involving sedative-adulterated drug exposures. As a CRM, it supports LC-MS/MS or GC-MS methods while addressing metabolite identification, calibration, and matrix-related accuracy challenges.