Teriflunomide-d4 is primarily used in research and development as an internal standard in analytical chemistry, particularly in mass spectrometry. Its deuterated structure allows for precise quantification and tracking of the non-deuterated form, teriflunomide, in biological samples. This is crucial for pharmacokinetic studies, where understanding the absorption, distribution, metabolism, and excretion of teriflunomide in the body is essential. Additionally, it aids in the development and validation of sensitive and accurate analytical methods for therapeutic drug monitoring, ensuring optimal dosing and efficacy in patients undergoing treatment for conditions like multiple sclerosis. Its use enhances the reliability of data in clinical and preclinical studies, contributing to advancements in medical research and patient care.