Indomethacin-d4 is primarily used in research and analytical laboratories as an internal standard in mass spectrometry and NMR studies. Its deuterated form allows for precise tracking and quantification of non-deuterated indomethacin in complex biological samples, such as blood or plasma, due to its nearly identical chemical properties but distinct mass. This application is crucial in pharmacokinetic studies to understand drug metabolism, distribution, and excretion. Additionally, it aids in the development and validation of analytical methods for detecting indomethacin in pharmaceutical formulations and clinical settings, ensuring accuracy and reliability in measurements.