Eicosapentaenoyl Ethanolamide-d4 (EPEA-d4) is primarily used as an internal standard in analytical chemistry, particularly in mass spectrometry and liquid chromatography-mass spectrometry (LC-MS). Its deuterated structure allows for precise quantification of its non-deuterated counterpart, EPEA, in biological samples. This application is crucial in research focused on endocannabinoid systems and lipid metabolism, where accurate measurement of EPEA levels is essential for understanding its role in inflammation, neuroprotection, and other physiological processes. Additionally, EPEA-d4 aids in the development of diagnostic tools and therapeutic strategies by providing reliable reference data in clinical and preclinical studies.