Used as an internal standard in mass spectrometry for the accurate quantification of domperidone in biological samples such as plasma, serum, or urine. Its deuterated structure allows it to closely mimic the behavior of non-labeled domperidone during sample extraction and analysis, improving measurement precision and reliability. Commonly applied in pharmacokinetic studies, bioavailability assessments, and therapeutic drug monitoring where consistent and sensitive detection is required. Also utilized in forensic toxicology and clinical research to distinguish between endogenous compounds and administered drug, minimizing matrix effects and instrument variability.