Ezetimibe D4 is primarily used as an internal standard in analytical chemistry for the quantification of ezetimibe in biological samples. It plays a crucial role in ensuring accuracy and precision in mass spectrometry and high-performance liquid chromatography (HPLC) analyses. By providing a stable and isotopically labeled reference, it aids in distinguishing the analyte from potential interferences, enhancing the reliability of pharmacokinetic studies and drug monitoring. This application is particularly valuable in clinical research and pharmaceutical development, where precise measurement of ezetimibe concentrations is essential for evaluating drug efficacy, safety, and metabolism.