Pimozide-d4, a deuterated form of pimozide, is primarily used in research and analytical applications as an internal standard in mass spectrometry. Its stable isotopic labeling allows for precise quantification of pimozide in biological samples, aiding in pharmacokinetic studies and drug metabolism research. This compound is particularly valuable in ensuring accuracy and reliability in the analysis of pimozide concentrations, supporting the development of therapeutic monitoring and toxicological assessments. Additionally, it helps in distinguishing the parent drug from its metabolites, enhancing the understanding of its pharmacological behavior in vivo.